Reference
Glossary
430 key terms from across Fathomly Guides, each defined in a sentence and linked to the guide that explains it in full.
430 terms from Fathomly Guides
A
- Abbasid Caliphate
- The dynasty that ruled much of the Islamic world from 750, with its capital at Baghdad.Explained in The Islamic Golden Age
- Aerobic
- Using oxygen to produce energy.Explained in The science of exercise
- Al-Andalus
- The parts of the Iberian Peninsula under Muslim rule in the Middle Ages.Explained in The Islamic Golden Age
- Allele
- One of the alternative versions of a gene.Explained in Evolution by natural selection, Genetics and inheritance
- Alveoli
- Tiny air sacs in the lungs where gas exchange happens.Explained in Human body systems, and how they cooperate
- Amplitude
- The size of a wave's vibration, related to loudness.Explained in Sound and hearing
- Anchoring
- Being pulled toward the first number or estimate encountered.Explained in Cognitive biases that distort your thinking
- Anode
- The electrode that releases electrons during discharge.Explained in Batteries and energy storage
- Antagonistic pair
- Two muscles that pull in opposite directions, since muscles cannot push.Explained in Human body systems, and how they cooperate
- Antibiotic
- A medicine that kills bacteria or stops them multiplying.Explained in Antibiotics and antibiotic resistance
- Antibody
- A protein made by B cells that binds a specific antigen.Explained in The immune system
- Antigen
- A molecule that the immune system can recognise.Explained in The immune system
- Antimicrobial resistance
- The ability of microbes to survive medicines designed to kill them.Explained in Antibiotics and antibiotic resistance
- Apex predator
- A predator at the top of a food chain with no natural predators of its own.Explained in Predators and prey
- Aposematism
- Warning colouration that signals an animal is dangerous or distasteful.Explained in Predators and prey
- Appeasement
- Making concessions to an aggressive power in the hope of avoiding war.Explained in The Second World War
- APR
- Annual percentage rate, the yearly cost of borrowing.Explained in Personal finance basics
- Aquifer
- An underground layer of rock or sediment that holds groundwater.Explained in The water cycle
- Arch
- A curved structure that spans an opening and carries weight to its sides.Explained in Architecture through the ages
- Armistice
- An agreement to stop fighting, which ended the war on 11 November 1918.Explained in The First World War
- Atoll
- A ring-shaped reef surrounding a lagoon.Explained in Coral reefs
- Atomic clock
- A clock that keeps time using the regular vibrations of atoms.Explained in How GPS works
- Atomic number
- The number of protons, which defines the element.Explained in Atoms and the periodic table
- ATP
- Adenosine triphosphate, the molecule cells use for energy.Explained in The science of exercise
- Atrium
- An upper chamber of the heart that receives blood.Explained in The heart and circulation
- Attention residue
- The part of your attention still occupied by a previous task after moving on.Explained in Attention, and why multitasking fails
- Availability heuristic
- Judging likelihood by how easily examples come to mind.Explained in Cognitive biases that distort your thinking
- Axis
- The alliance of Germany, Italy and Japan.Explained in The Second World War
B
- Bacteriophage
- A virus that infects bacteria.Explained in Viruses and bacteria
- Bacterium
- A single-celled organism without a nucleus.Explained in Viruses and bacteria
- Baroque
- A dramatic, ornate style of the seventeenth century.Explained in A short history of Western art
- Basal ganglia
- Brain structures involved in forming and running habits.Explained in How habits form
- Base
- The number of distinct digits a number system uses.Explained in Numbers and number systems
- Base rate
- How common something is in the population before any evidence is considered.Explained in Probability and statistics, and how they get misused
- Bioluminescence
- Light produced by living organisms through a chemical reaction.Explained in The ocean and its zones
- Biome
- A large ecological community defined by its climate and vegetation.Explained in Climate zones and biomes
- Biosignature
- A measurable sign that could indicate the presence of life.Explained in Exoplanets and the search for life
- Bit
- A binary digit, 0 or 1, the smallest unit of data.Explained in How computers work
- Boiling point
- The temperature at which a liquid turns to gas at a given pressure.Explained in States of matter
- Broadsheet
- A single large printed sheet, used for news and announcements.Explained in The printing press and the information revolution
- Bronsted-Lowry acid
- A proton donor.Explained in Acids, bases and the pH scale
- Budget
- A plan for how income will be spent and saved.Explained in Personal finance basics
- Buffer
- A mixture of a weak acid and its conjugate base that resists pH change.Explained in Acids, bases and the pH scale
C
- Caffeine
- A stimulant found in coffee and tea that reduces feelings of tiredness.Explained in The story of coffee and tea
- Camellia sinensis
- The plant whose leaves are used to make tea.Explained in The story of coffee and tea
- Canopy
- The dense upper layer of leaves and branches in a forest.Explained in Tropical rainforests
- Caravanserai
- A roadside inn providing shelter, storage and safety for travelling merchants.Explained in Trade routes and the exchange of ideas
- Caravel
- A small, manoeuvrable sailing ship developed by the Portuguese.Explained in The Age of Exploration
- Carbon sink
- Something that absorbs more carbon from the atmosphere than it releases.Explained in Tropical rainforests
- Care ethics
- An approach centred on relationships and responsiveness to others' needs.Explained in Theories of ethics: consequences, duties and virtues
- Carrying capacity
- The population size an environment can support over time.Explained in Ecosystems: energy, matter and why food chains are short
- Catalyst
- A substance that speeds a reaction by lowering activation energy and is not consumed.Explained in Reactions, equations and the mole
- Categorical imperative
- Kant's principle that one should act only on rules one could will to be universal.Explained in Theories of ethics: consequences, duties and virtues
- Cathode
- The electrode that receives electrons during discharge.Explained in Batteries and energy storage
- Chaturanga
- An early Indian form of chess.Explained in The history of chess
- Checkmate
- A position where the king is attacked and cannot escape, ending the game.Explained in The history of chess
- Chemosynthesis
- Making food from chemical energy rather than sunlight.Explained in The ocean and its zones
- Chess engine
- A computer program that analyses chess positions and plays moves.Explained in The history of chess
- Chiaroscuro
- The dramatic use of strong contrasts between light and dark.Explained in How to look at a painting
- Chord
- Three or more notes sounded together.Explained in How music works
- Chorleywood process
- A fast industrial breadmaking method developed in Britain in 1961.Explained in The history of bread
- Chunk
- A unit of meaning in working memory. Expertise makes chunks larger, not more numerous.Explained in How memory actually works
- Ciphertext
- Encrypted data that cannot be read without the key.Explained in Encryption and online security
- Circumnavigation
- A voyage all the way around the world.Explained in The Age of Exploration
- Climate
- The long-term average pattern of weather in a place.Explained in Climate zones and biomes
- Cochlea
- The spiral inner-ear structure that converts vibrations into nerve signals.Explained in Sound and hearing
- Codon
- A triplet of bases in messenger RNA specifying one amino acid.Explained in DNA, RNA and how a gene becomes a protein
- Coevolution
- When two species evolve in response to each other.Explained in Pollination and pollinators
- Columbian Exchange
- The transfer of crops, animals, people and diseases between the hemispheres after 1492.Explained in The Age of Exploration, Trade routes and the exchange of ideas
- Comparative advantage
- The ability to produce a good at a lower opportunity cost than others.Explained in International trade and globalisation
- Complementary pairing
- The rule that A pairs with T and C pairs with G.Explained in DNA, RNA and how a gene becomes a protein
- Composition
- The arrangement of elements within a work of art.Explained in How to look at a painting
- Compound interest
- Interest calculated on both the original amount and previously earned interest.Explained in Personal finance basics
- Condensation
- The change of water vapour into liquid droplets.Explained in The water cycle
- Confirmation bias
- Favouring evidence that supports an existing belief.Explained in Cognitive biases that distort your thinking
- Confounding variable
- A hidden factor that affects both variables in a correlation.Explained in Statistics in everyday life
- Congruent
- Identical in both shape and size.Explained in Geometry and trigonometry
- Conjugate base
- What remains after an acid donates its proton.Explained in Acids, bases and the pH scale
- Conquistador
- A Spanish or Portuguese soldier who took part in the conquest of the Americas.Explained in The Age of Exploration
- Consolidation
- The process of stabilising and integrating new memories, much of which happens during sleep.Explained in Sleep and the learning brain
- Containment
- The US policy of preventing the spread of communism.Explained in The Cold War
- Continuity editing
- Editing designed to keep space and time clear and cuts unobtrusive.Explained in The language of film
- Contour line
- A line on a map joining points of equal elevation.Explained in Reading maps: scale, projection and coordinates
- Coral bleaching
- The loss of symbiotic algae from corals under stress, turning them white.Explained in Coral reefs
- Cosmic microwave background
- Leftover radiation from the early universe.Explained in Stars, galaxies and the universe
- Cosmopolitanism
- The idea that all humans belong to a single community.Explained in Stoicism: the philosophy of what you can control
- CPU
- The central processing unit, which executes program instructions.Explained in How computers work
- Cross-pollination
- The transfer of pollen from one plant to another of the same species.Explained in Pollination and pollinators
- Cubism
- An early twentieth-century style showing objects from multiple viewpoints at once.Explained in A short history of Western art
- Cue
- A trigger that starts a habitual behaviour.Explained in How habits form
- Cuju
- An ancient Chinese ball-kicking game.Explained in The history of football
- Cuneiform
- The wedge-shaped Mesopotamian script, first used for accounting.Explained in The agricultural revolution and the first cities
- Current
- Rate of flow of charge, measured in amperes.Explained in Electricity and circuits
- Cyclic quadrilateral
- A four-sided shape with all vertices on a circle.Explained in Geometry and trigonometry
D
- D-Day
- The Allied landings in Normandy on 6 June 1944.Explained in The Second World War
- Decibel
- A logarithmic unit for sound intensity.Explained in Sound and hearing
- Decomposer
- An organism that breaks down dead material and returns nutrients to the ecosystem.Explained in Ecosystems: energy, matter and why food chains are short
- Deflation
- A sustained fall in the general price level.Explained in Money, inflation and how banks create deposits
- Delocalised electron
- An electron not tied to one atom, free to move through a structure.Explained in Chemical bonding and why substances behave differently
- Delta
- A landform built from sediment where a river enters a sea or lake.Explained in Rivers and river systems
- Demand pull inflation
- Rising prices caused by spending exceeding productive capacity.Explained in Money, inflation and how banks create deposits
- Demographic transition
- The shift from high birth and death rates to low birth and death rates.Explained in Population and cities
- Denaturation
- The unfolding of a protein's structure, often caused by heat or acid.Explained in The science of cooking
- Desertification
- The degradation of drylands into desert-like conditions.Explained in Deserts of the world
- Desirable difficulty
- A task hard enough to require real effort, which produces stronger long-term learning.Explained in How memory actually works
- Détente
- The easing of Cold War tension in the 1970s.Explained in The Cold War
- Dew point
- The temperature at which air becomes saturated and water condenses.Explained in Climate and weather: the system that moves heat
- Dichotomy of control
- The distinction between what is up to us and what is not.Explained in Stoicism: the philosophy of what you can control
- Diegetic sound
- Sound that originates within the world of the story.Explained in The language of film
- Dietary fibre
- Plant material that the body cannot fully digest, which supports gut health.Explained in Nutrition basics
- Discriminant
- The part under the square root in the quadratic formula, which tells you how many real roots exist.Explained in Algebra: what the letters actually mean
- Diversification
- Spreading money across different investments to reduce risk.Explained in Personal finance basics
- DNS
- The system that translates domain names into IP addresses.Explained in How the internet works
- Domestication
- The long process of altering species through selective breeding for human use.Explained in The agricultural revolution and the first cities
- Doppler effect
- The change in observed frequency due to relative motion.Explained in Waves, sound and light
- Drag
- The air resistance that opposes an aircraft's motion.Explained in The history of flight
- Drainage basin
- The area of land that drains into a particular river.Explained in Rivers and river systems
- Dwarf planet
- A round body orbiting the sun that has not cleared its orbital neighbourhood.Explained in A tour of the planets
E
- Efficiency
- Useful energy output divided by total energy input.Explained in Energy, work and power
- Elasticity
- How responsive quantity is to a change in price.Explained in Supply, demand and what prices are really doing
- Electrolyte
- The material that lets ions move between electrodes.Explained in Batteries and energy storage
- Electromagnet
- A magnet created by electric current flowing through a coil.Explained in Magnetism
- Electronegativity
- How strongly an atom attracts shared electrons in a bond.Explained in Atoms and the periodic table
- Emotion
- A brief, coordinated response to a significant event, involving feelings, body and behaviour.Explained in Emotions and how they work
- Emulsion
- A mixture of two liquids that do not normally combine, held together by an emulsifier.Explained in The science of cooking
- Encoding
- Turning an experience into a memory trace the brain can store.Explained in How memory actually works
- Endosymbiosis
- The theory that mitochondria and chloroplasts descend from engulfed bacteria.Explained in The cell: the unit everything living is built from
- Energy density
- How much energy a battery stores per unit of mass or volume.Explained in Batteries and energy storage
- Entropy
- A measure of how spread out and unusable energy has become.Explained in Energy, work and power
- Epicentre
- The surface point directly above an earthquake's focus.Explained in Plate tectonics: why continents move, Volcanoes and earthquakes
- Epidemiology
- The study of how diseases occur and spread in populations.Explained in Public health and epidemics
- Epiphyte
- A plant, such as many orchids, that grows on another plant without harming it.Explained in Tropical rainforests
- Epistemology
- The study of knowledge and justified belief.Explained in What is philosophy?
- Equilibrium
- The price at which quantity supplied equals quantity demanded.Explained in Supply, demand and what prices are really doing
- Erg
- A large area covered with wind-blown sand dunes.Explained in Deserts of the world
- Essential amino acid
- An amino acid the body cannot make and must obtain from food.Explained in Nutrition basics
- Eudaimonia
- Aristotle's idea of human flourishing, the goal of a virtuous life.Explained in Theories of ethics: consequences, duties and virtues
- Eurogame
- A style of strategy board game popularised in Germany.Explained in The story of board games
- Evaporation
- The change of liquid water into water vapour.Explained in The water cycle
- Exoplanet
- A planet orbiting a star other than the sun.Explained in Exoplanets and the search for life
- Exothermic
- A reaction that releases more energy than it absorbs.Explained in Reactions, equations and the mole
- Expression
- A combination of numbers and letters with no equals sign.Explained in Algebra: what the letters actually mean
- Extrinsic motivation
- Drive that comes from outside the activity, such as grades or money.Explained in Motivation: what actually sustains it
F
- Factory Acts
- British laws regulating working hours and conditions, especially for children.Explained in The Industrial Revolution
- Factory system
- Production in a central workplace with machines, set hours and supervised labour.Explained in The Industrial Revolution
- Fair trade
- A certification system aimed at better prices and conditions for producers.Explained in The story of coffee and tea
- Fallacy
- A common error in reasoning that makes an argument unreliable.Explained in Logic and good reasoning
- Fault
- A fracture in rock along which movement occurs.Explained in Volcanoes and earthquakes
- Federalism
- Division of authority between national and regional governments.Explained in How governments are structured
- Fermentation
- The breakdown of substances by microorganisms, producing acids, gases or alcohol.Explained in Fermentation: bread, cheese, yogurt and more
- Ferromagnetism
- Strong magnetism in materials like iron, caused by aligned domains.Explained in Magnetism
- Fiat money
- Currency with value by acceptance and law rather than commodity backing.Explained in Money, inflation and how banks create deposits
- FIFA
- The international governing body of football, founded in 1904.Explained in The history of football
- Fight-or-flight response
- The body's rapid reaction to perceived threat.Explained in Emotions and how they work
- Fitness
- Relative reproductive success in a given environment.Explained in Evolution by natural selection
- Five Pillars
- The core practices of Islam.Explained in The world's major religions
- Flatbread
- Bread made without leavening, or with very little.Explained in The history of bread
- Flying buttress
- An external arched support that carries thrust away from a wall.Explained in Architecture through the ages
- Flyway
- A major route used by migratory birds.Explained in Animal migration
- Fold
- A bend in rock layers caused by compression.Explained in How mountains form
- Football Association
- The English governing body founded in 1863 that codified the rules.Explained in The history of football
- Frame rate
- The number of still images shown per second.Explained in The language of film
- Frequency
- The number of vibrations per second, which determines pitch.Explained in How music works, Sound and hearing
- Front
- The boundary between two air masses of different temperature and humidity.Explained in Climate and weather: the system that moves heat
- Frost line
- The distance from a star beyond which ices can condense.Explained in The solar system, stars and the life cycle of matter
- Function
- A rule assigning exactly one output to each input.Explained in Algebra: what the letters actually mean
- Functional group
- A group of atoms that gives a molecule characteristic reactions.Explained in Organic chemistry basics
- Fusion
- Joining light nuclei into heavier ones, releasing energy.Explained in The solar system, stars and the life cycle of matter
G
- Gas giant
- A large planet made mainly of hydrogen and helium, like Jupiter.Explained in A tour of the planets
- General will
- Rousseau's idea of the collective will aimed at the common good.Explained in Political philosophy and the social contract
- Generator
- A machine that converts motion into electricity using electromagnetic induction.Explained in Electricity and the power grid
- Genetic drift
- Random change in allele frequencies, strongest in small populations.Explained in Evolution by natural selection
- Genotype
- The set of alleles an organism carries.Explained in Genetics and inheritance
- Giant impact hypothesis
- The theory that the Moon formed from debris of a collision with the early Earth.Explained in The Moon
- Gluten
- An elastic protein network formed from wheat flour and water.Explained in The science of cooking
- GNSS
- Global navigation satellite system, the general term for GPS and its counterparts.Explained in How GPS works
- Grain dole
- The Roman system of distributing grain or bread to citizens.Explained in The history of bread
- Grid frequency
- The rate at which alternating current reverses, kept near 50 or 60 cycles per second.Explained in Electricity and the power grid
- Guild
- An association of merchants or craftsmen that regulated a trade in a town.Explained in The Middle Ages in Europe
H
- Habit
- A behaviour triggered automatically by a context or cue.Explained in How habits form
- Habit stacking
- Linking a new habit to an existing routine.Explained in How habits form
- Habitable zone
- The range of orbits where liquid water could exist on a planet's surface.Explained in Exoplanets and the search for life
- Hash
- A fixed-length fingerprint of data that cannot practically be reversed.Explained in Encryption and online security
- Herd immunity
- Protection that arises when enough of a population is immune to a disease.Explained in Public health and epidemics
- Heuristic
- A mental shortcut that produces fast, usually adequate judgements.Explained in Cognitive biases that distort your thinking
- Hindsight bias
- Seeing an outcome as predictable once you know it happened.Explained in Cognitive biases that distort your thinking
- Holocaust
- The Nazi genocide of about six million European Jews.Explained in The Second World War
- Homeostasis
- Keeping internal conditions stable despite external change.Explained in Human body systems, and how they cooperate
- Homologous structure
- A feature shared by species because both inherited it from a common ancestor.Explained in Evolution by natural selection
- Hotspot
- An area of volcanic activity fed by a plume of hot mantle material.Explained in How mountains form
- House of Wisdom
- A Baghdad centre of translation and scholarship linked to the Abbasid court.Explained in The Islamic Golden Age
- Hydrocarbon
- A compound made only of carbon and hydrogen.Explained in Organic chemistry basics
- Hydrogen bond
- A strong intermolecular attraction involving hydrogen bonded to N, O or F.Explained in Chemical bonding and why substances behave differently
- Hypertension
- Persistently high blood pressure.Explained in The heart and circulation
- Hypertrophy
- The growth of muscle fibres in response to training.Explained in The science of exercise
- Hyphae
- The individual microscopic threads of a fungus.Explained in Fungi: the hidden kingdom
- Hypotenuse
- The side opposite the right angle, always the longest.Explained in Geometry and trigonometry
I
- Ice giant
- A giant planet rich in water, ammonia and methane, like Uranus and Neptune.Explained in A tour of the planets
- Identity
- An equation true for every value of the variable.Explained in Algebra: what the letters actually mean
- Imaginary unit
- The number i, defined as the square root of minus 1.Explained in Numbers and number systems
- Impasto
- Paint applied thickly enough that brushstrokes stand out from the surface.Explained in How to look at a painting
- Impressionism
- A nineteenth-century movement focused on light, colour and everyday modern life.Explained in A short history of Western art
- Impulse
- Force multiplied by the time it acts, equal to change in momentum.Explained in Motion and forces
- Inattentional blindness
- Failing to notice a visible object because attention was directed elsewhere.Explained in Attention, and why multitasking fails
- Incunabula
- Books printed in Europe before 1501.Explained in The printing press and the information revolution
- Independent events
- Events where one occurring does not change the probability of the other.Explained in Probability and statistics, and how they get misused
- Induction
- Reasoning from particular observations to probable general conclusions.Explained in Logic and good reasoning
- Inertia
- The tendency of a body to resist changes in its motion, measured by mass.Explained in Motion and forces
- Interleaving
- Mixing different problem types in one practice session.Explained in How to solve a problem you have not seen before
- Intrinsic motivation
- Drive that comes from the activity itself, such as interest or enjoyment.Explained in Motivation: what actually sustains it
- Intron
- A non-coding section removed from the initial RNA transcript before translation.Explained in DNA, RNA and how a gene becomes a protein
- Invariant
- A quantity that remains unchanged throughout a process.Explained in How to solve a problem you have not seen before
- IOC
- The International Olympic Committee, which governs the Olympic movement.Explained in The Olympic Games
- Ionic lattice
- A repeating three-dimensional arrangement of oppositely charged ions.Explained in Chemical bonding and why substances behave differently
- Ionisation energy
- The energy needed to remove an electron from an atom.Explained in Atoms and the periodic table
- IP address
- The numerical address that identifies a device on the internet.Explained in How the internet works
- Irrational number
- A real number that cannot be written as a fraction of integers.Explained in Numbers and number systems
- Isomer
- A compound with the same formula as another but a different structure.Explained in Organic chemistry basics
- Isotope
- An atom of the same element with a different neutron count.Explained in Atoms and the periodic table
J
- Jet engine
- An engine that produces thrust by expelling hot, fast-moving gas.Explained in The history of flight
- Judicial review
- Courts assessing whether laws or acts conform to the constitution.Explained in How governments are structured
K
- Karma
- In Indian religions, the principle that actions produce consequences, including in future lives.Explained in The world's major religions
- Khan
- A title for a ruler among Mongol and Turkic peoples.Explained in The Mongol Empire
- Kilowatt hour
- Energy equal to one kilowatt sustained for one hour.Explained in Electricity and circuits
- Koji
- A mould used in East Asian fermentation of soy sauce, miso and sake.Explained in Fermentation: bread, cheese, yogurt and more
- Kurultai
- A Mongol assembly of leaders that chose khans and decided major campaigns.Explained in The Mongol Empire
L
- Lactic acid bacteria
- Bacteria that produce lactic acid, used in yogurt, cheese and pickled vegetables.Explained in Fermentation: bread, cheese, yogurt and more
- Latent heat
- Energy absorbed or released during a change of state without a change in temperature.Explained in States of matter
- Latitude
- Distance north or south of the equator, measured in degrees.Explained in Reading maps: scale, projection and coordinates
- Leavening
- The process of making dough rise, usually with yeast or chemical agents.Explained in The history of bread
- Legitimacy
- The accepted right of a government to rule.Explained in Revolutions and the making of the modern state
- Lift
- The upward force produced by air flowing over a wing.Explained in The history of flight
- Light-year
- The distance light travels in one year, about 9.5 trillion kilometres.Explained in Stars, galaxies and the universe
- Limiting reactant
- The reactant that runs out first and caps the amount of product.Explained in Reactions, equations and the mole
- Linear perspective
- A system of creating depth using lines that converge at a vanishing point.Explained in How to look at a painting
- Longitude
- Distance east or west of the prime meridian, measured in degrees.Explained in Reading maps: scale, projection and coordinates
M
- Maat
- The Egyptian concept of truth, justice and balance that rulers were meant to uphold.Explained in Ancient Egypt: three thousand years on the Nile
- Macronutrient
- A nutrient needed in large amounts, such as carbohydrate, protein or fat.Explained in Nutrition basics
- Madrasa
- A college for Islamic learning, often funded by a charitable endowment.Explained in The Islamic Golden Age
- Magma
- Molten rock beneath the surface; called lava once it erupts.Explained in Volcanoes and earthquakes
- Magna Carta
- A 1215 charter limiting the English king's power and asserting the rule of law.Explained in The Middle Ages in Europe
- Magnetic field
- The region around a magnet or current where magnetic forces act.Explained in Magnetism
- Magnetoreception
- The ability to sense Earth's magnetic field.Explained in Animal migration
- Magnetosphere
- The region around a planet controlled by its magnetic field.Explained in Magnetism
- Maillard reaction
- A reaction between amino acids and sugars that produces browning and flavour.Explained in The science of cooking
- Mancala
- A family of games played by sowing seeds around rows of pits.Explained in The story of board games
- Manor
- An estate held by a lord, including the land farmed by peasants who owed him labour and dues.Explained in The Middle Ages in Europe
- Map projection
- A method of representing Earth's curved surface on a flat map.Explained in Reading maps: scale, projection and coordinates
- Margin of error
- The range of uncertainty around an estimate from a sample.Explained in Statistics in everyday life
- Maria
- Dark plains on the Moon formed by ancient lava flows.Explained in The Moon
- Marine snow
- Organic particles that sink from upper waters into the deep sea.Explained in The ocean and its zones
- Mastery goal
- A goal aimed at becoming more capable, as opposed to appearing capable.Explained in Motivation: what actually sustains it
- Meander
- A looping bend in a river.Explained in Rivers and river systems
- Median
- The middle value of an ordered dataset, resistant to outliers.Explained in Probability and statistics, and how they get misused, Statistics in everyday life
- Megacity
- A metropolitan area with more than 10 million people.Explained in Population and cities
- Meiosis
- Division producing four genetically varied cells with half the chromosome number.Explained in The cell: the unit everything living is built from, Genetics and inheritance
- Memory cell
- A long-lived lymphocyte that allows a faster response to a repeat infection.Explained in The immune system
- Metamorphic rock
- Rock changed by heat and pressure without melting.Explained in Plate tectonics: why continents move
- Metaphysics
- The branch of philosophy that studies the fundamental nature of reality.Explained in What is philosophy?
- Microbiome
- The community of microorganisms living in a particular environment, such as the gut.Explained in Viruses and bacteria
- Micronutrient
- A vitamin or mineral needed in small amounts.Explained in Nutrition basics
- Mimicry
- When one species evolves to resemble another.Explained in Predators and prey
- Mitochondria
- Structures in cells that produce ATP using oxygen.Explained in The science of exercise
- Mixed constitution
- A system combining monarchic, aristocratic and popular elements.Explained in Greece and Rome: the political inheritance
- Mob football
- Unregulated medieval football played by large crowds.Explained in The history of football
- Modernism
- A twentieth-century movement emphasising function, simplicity and new materials.Explained in Architecture through the ages
- Mole
- A counting unit equal to about 6.02 times ten to the twenty third particles.Explained in Reactions, equations and the mole
- Moluccas
- The Spice Islands of eastern Indonesia, once the only source of cloves and nutmeg.Explained in The spice trade
- Monetary policy
- Central bank management of interest rates and money conditions.Explained in Money, inflation and how banks create deposits
- Monopoly
- Exclusive control over the supply of a good.Explained in The spice trade
- Monotheism
- Belief in a single God.Explained in The world's major religions
- Monsoon
- A seasonal wind reversal that made predictable Indian Ocean sailing possible.Explained in Trade routes and the exchange of ideas, The spice trade
- Montage
- An editing technique that builds meaning by juxtaposing shots.Explained in The language of film
- Mood
- A longer-lasting, less specific emotional state.Explained in Emotions and how they work
- Movable type
- Individual letters that can be arranged, printed and reused.Explained in The printing press and the information revolution
- Multi-stage rocket
- A rocket that drops empty sections during flight to save weight.Explained in The history of space exploration
- Multipath
- Error caused when a signal reflects off surfaces before arriving.Explained in How GPS works
- Mutually assured destruction
- The idea that nuclear war would destroy both sides, deterring either from starting it.Explained in The Cold War
- Mycelium
- The network of fungal threads that makes up most of a fungus.Explained in Fungi: the hidden kingdom
- Mycorrhiza
- A mutually beneficial partnership between a fungus and plant roots.Explained in Fungi: the hidden kingdom
N
- Nationalism
- The belief that a people sharing culture and history should form a self-governing state.Explained in Revolutions and the making of the modern state
- Natural rights
- Rights people possess by nature, not granted by governments.Explained in Political philosophy and the social contract
- Nectar
- A sugary liquid flowers produce to reward pollinators.Explained in Pollination and pollinators
- Negative feedback
- A loop that reverses a detected change and returns a value toward its set point.Explained in Human body systems, and how they cooperate
- Neocolonialism
- Continued economic or political control over a formally independent country.Explained in Decolonization and the new nations
- Neolithic
- The period of early farming, before widespread metal tools.Explained in The agricultural revolution and the first cities
- Neuron
- A nerve cell that transmits electrical and chemical signals.Explained in The brain
- Neuroplasticity
- The brain's ability to reorganise its connections.Explained in The brain
- Neurotransmitter
- A chemical that carries a signal across the gap between neurons.Explained in Human body systems, and how they cooperate, The brain
- Niche
- The role and position a species has in its environment.Explained in Tropical rainforests
- Nilometer
- A structure used to measure the height of the Nile flood.Explained in Ancient Egypt: three thousand years on the Nile
- Nirvana
- In Buddhism, liberation from suffering and the cycle of rebirth.Explained in The world's major religions
- No man's land
- The ground between opposing trench lines.Explained in The First World War
- Non-Aligned Movement
- A group of states that refused formal alliance with either Cold War bloc.Explained in Decolonization and the new nations
- Novel
- A long fictional narrative written in prose.Explained in The story of the novel
- Nuclear fusion
- The joining of atomic nuclei, releasing energy, which powers stars.Explained in Stars, galaxies and the universe
- Nucleotide
- The repeating unit of DNA: a phosphate, a sugar and a base.Explained in DNA, RNA and how a gene becomes a protein
O
- Oasis
- A fertile spot in a desert where groundwater reaches the surface.Explained in Deserts of the world
- Olympiad
- The four-year period between Olympic Games.Explained in The Olympic Games
- Operating system
- Software that manages hardware and runs other programs.Explained in How computers work
- Opium Wars
- Nineteenth-century wars between Britain and China over the opium trade.Explained in The story of coffee and tea
- Opportunity cost
- The value of the best alternative given up by a choice.Explained in Supply, demand and what prices are really doing
- Organelle
- A specialised structure inside a cell that performs a particular function.Explained in The cell: the unit everything living is built from
- Osmosis
- The movement of water across a selectively permeable membrane down its concentration gradient.Explained in The cell: the unit everything living is built from
- Overjustification effect
- The drop in intrinsic interest that can follow being rewarded for something you already enjoyed.Explained in Motivation: what actually sustains it
P
- Packet
- A small unit of data with a header containing addressing information.Explained in How the internet works
- Pandemic
- An epidemic that spreads across multiple countries or continents.Explained in Public health and epidemics
- Paralympics
- The major international multi-sport event for athletes with disabilities.Explained in The Olympic Games
- Partition
- The 1947 division of British India into India and Pakistan.Explained in Decolonization and the new nations
- Pathogen
- A microorganism that can cause disease.Explained in The immune system
- Pax Mongolica
- The period of relatively safe travel and trade across the Mongol-ruled lands.Explained in The Mongol Empire
- Pentathlon
- An event combining five contests, part of the ancient Games.Explained in The Olympic Games
- Permafrost
- Ground that stays frozen for at least two consecutive years.Explained in Climate zones and biomes
- Pharaoh
- The king of Egypt, seen as divine and responsible for cosmic order.Explained in Ancient Egypt: three thousand years on the Nile
- Phenotype
- The observable traits that result from genes and environment.Explained in Genetics and inheritance
- Philopatry
- The tendency to return to one's birthplace to breed.Explained in Animal migration
- Photon
- A quantum of electromagnetic energy, proportional to frequency.Explained in Waves, sound and light
- Phytoplankton
- Microscopic drifting organisms that photosynthesise in surface waters.Explained in The ocean and its zones
- Place value
- A system where a digit's value depends on its position.Explained in Numbers and number systems
- Plasma
- An ionised gas made of charged particles.Explained in States of matter
- Plasmid
- A small loop of DNA that bacteria can share, often carrying resistance genes.Explained in Antibiotics and antibiotic resistance
- Polar bond
- A bond where electrons are unevenly shared due to differing electronegativity.Explained in Chemical bonding and why substances behave differently
- Polis
- An independent Greek city-state and its surrounding territory.Explained in Greece and Rome: the political inheritance
- Polymer
- A large molecule made of many repeating units.Explained in Organic chemistry basics
- Polyp
- The individual soft-bodied animal that makes up a coral colony.Explained in Coral reefs
- Positive feedback
- A response that amplifies the original change.Explained in Climate and weather: the system that moves heat
- Post and lintel
- A structure of vertical supports with a horizontal beam across them.Explained in Architecture through the ages
- Potential difference
- Energy transferred per unit charge between two points.Explained in Electricity and circuits
- Power
- Rate of energy transfer, measured in watts.Explained in Energy, work and power
- Preferred indifferents
- Things like health and wealth that are reasonable to seek but not truly good in themselves.Explained in Stoicism: the philosophy of what you can control
- Premise
- A statement that an argument assumes in order to reach a conclusion.Explained in What is philosophy?
- Price ceiling
- A legal maximum price, which causes shortage if set below equilibrium.Explained in Supply, demand and what prices are really doing
- Prokaryote
- A cell with no nucleus or membrane-bound organelles, such as a bacterium.Explained in The cell: the unit everything living is built from
- Proportional representation
- Allocating seats in proportion to votes received.Explained in How governments are structured
- Protectionism
- Policies that restrict imports to shield domestic industries.Explained in International trade and globalisation
- Proxy war
- A conflict in which rival powers support opposing sides rather than fighting directly.Explained in The Cold War
- Public key
- A key shared openly, used to encrypt messages or check signatures.Explained in Encryption and online security
- Pyroclastic flow
- A fast-moving current of hot gas and volcanic debris.Explained in Volcanoes and earthquakes
R
- Radiative forcing
- A change in the energy balance between incoming and outgoing radiation.Explained in Climate and weather: the system that moves heat
- Rain shadow
- A dry area on the side of a mountain range facing away from moist winds.Explained in How mountains form
- Realism
- A literary approach that depicts everyday life and society accurately.Explained in The story of the novel
- Reappraisal
- Changing how one interprets a situation to change its emotional impact.Explained in Emotions and how they work
- Redshift
- The stretching of light toward longer wavelengths, indicating recession.Explained in The solar system, stars and the life cycle of matter, Stars, galaxies and the universe
- Refraction
- The bending of a wave caused by a change in speed between media.Explained in Waves, sound and light
- REM sleep
- A stage that lengthens toward morning, linked to integration, pattern finding and skills.Explained in Sleep and the learning brain
- Renaissance
- A cultural revival of classical learning and art beginning in fourteenth- and fifteenth-century Italy.Explained in A short history of Western art
- Replacement level
- The fertility rate, about 2.1, at which a population replaces itself.Explained in Population and cities
- Reproduction number
- The average number of people infected by each case.Explained in Public health and epidemics
- Resistance
- Opposition to current, measured in ohms.Explained in Electricity and circuits
- Resultant force
- The vector sum of all forces acting on a body.Explained in Motion and forces
- Retrieval practice
- Recalling material from memory rather than reviewing it.Explained in How to solve a problem you have not seen before
- Rosetta Stone
- A decree in three scripts that made it possible to read hieroglyphs again.Explained in Ancient Egypt: three thousand years on the Nile
- Router
- A device that forwards packets between networks toward their destination.Explained in How the internet works
S
- Satellite
- An object that orbits a planet, either natural like the Moon or artificial.Explained in The history of space exploration
- Seafloor spreading
- Creation of new oceanic crust at mid-ocean ridges.Explained in Plate tectonics: why continents move
- Self-determination
- The right of a people to choose their own political status and government.Explained in Decolonization and the new nations
- Semi-conservative
- Replication in which each new molecule keeps one original strand.Explained in DNA, RNA and how a gene becomes a protein
- Senet
- An ancient Egyptian race game with religious meaning.Explained in The story of board games
- Separate condenser
- James Watt's improvement that made steam engines far more fuel efficient.Explained in The Industrial Revolution
- Separation of powers
- Dividing government functions so each can check the others.Explained in Revolutions and the making of the modern state, How governments are structured
- Serf
- A peasant legally bound to a manor and its lord.Explained in The Middle Ages in Europe
- Serialisation
- Publishing a long work in instalments over time.Explained in The story of the novel
- Shatranj
- The Persian and Arabic form of chess.Explained in The history of chess
- Similar
- Same shape, proportional sizes, equal angles.Explained in Geometry and trigonometry
- Sinoatrial node
- The heart's natural pacemaker, which starts each heartbeat.Explained in The heart and circulation
- Slow-wave sleep
- Deep sleep, concentrated early in the night, linked to consolidating facts and events.Explained in Sleep and the learning brain
- Social contract
- The idea that political authority rests on an agreement among the governed.Explained in Political philosophy and the social contract
- Sortition
- Selecting officials by lottery rather than election.Explained in Greece and Rome: the political inheritance
- Sound
- A valid argument with true premises.Explained in Logic and good reasoning
- Sound barrier
- The sharp rise in drag an aircraft meets near the speed of sound.Explained in The history of flight
- Space debris
- Defunct satellites, rocket stages and fragments orbiting Earth.Explained in The history of space exploration
- Space station
- A crewed spacecraft that remains in orbit for long periods.Explained in The history of space exploration
- Speciation
- The process by which one population splits into two that can no longer interbreed.Explained in Evolution by natural selection
- Spore
- A small reproductive cell that can grow into a new fungus.Explained in Fungi: the hidden kingdom
- Spring tide
- An especially large tide when the sun and Moon line up.Explained in The Moon
- Standard deviation
- A measure of typical distance from the mean.Explained in Probability and statistics, and how they get misused, Statistics in everyday life
- State of nature
- A hypothetical condition of human life without government.Explained in Political philosophy and the social contract
- Stewardship
- Careful, appropriate use of antibiotics to slow resistance.Explained in Antibiotics and antibiotic resistance
- Stigma
- The part of a flower that receives pollen.Explained in Pollination and pollinators
- Stoa
- A covered colonnade in Athens where Zeno taught, giving Stoicism its name.Explained in Stoicism: the philosophy of what you can control
- Stopover site
- A place where migrating animals rest and refuel during their journey.Explained in Animal migration
- Stream of consciousness
- A technique presenting a character's continuous flow of thoughts.Explained in The story of the novel
- Strong acid
- One that dissociates essentially completely in water.Explained in Acids, bases and the pH scale
- Subduction
- One plate sinking beneath another into the mantle.Explained in Plate tectonics: why continents move, How mountains form
- Sublimation
- A change directly from solid to gas.Explained in States of matter
- Substation
- A facility that changes voltage levels and routes power in the grid.Explained in Electricity and the power grid
- Succession
- The sequence of community change in an area over time.Explained in Ecosystems: energy, matter and why food chains are short
- Supernova
- The explosive death of a massive star.Explained in The solar system, stars and the life cycle of matter
- Supply chain
- The network of producers and transport involved in making and delivering a product.Explained in International trade and globalisation
- Surplus
- Food produced beyond immediate need, which can be stored or taxed.Explained in The agricultural revolution and the first cities
- Switch cost
- The time and accuracy penalty paid each time you move between tasks.Explained in Attention, and why multitasking fails
- Symmetric encryption
- Encryption where the same key is used to encrypt and decrypt.Explained in Encryption and online security
- Synapse
- The junction where one neuron communicates with another.Explained in The brain
- Syncopation
- Emphasis on beats or parts of beats that are normally unstressed.Explained in How music works
T
- Taiga
- The boreal coniferous forest of the far north.Explained in Climate zones and biomes
- Tariff
- A tax on imported goods.Explained in International trade and globalisation
- Terminal velocity
- The steady speed reached when drag balances weight.Explained in Motion and forces
- Terrestrial planet
- A rocky planet with a solid surface, like Earth or Mars.Explained in A tour of the planets
- Testing effect
- The finding that retrieving information strengthens memory more than restudying it.Explained in How memory actually works
- Thought experiment
- An imagined scenario used to test a concept or theory.Explained in What is philosophy?
- Tidal locking
- When a body's rotation matches its orbit, so it always shows the same face.Explained in The Moon
- Timbre
- The characteristic sound quality of a voice or instrument.Explained in How music works
- Total fertility rate
- The average number of children a woman would have over her lifetime.Explained in Population and cities
- Transformer
- A device that raises or lowers the voltage of alternating current.Explained in Electricity and the power grid
- Transistor
- An electronic switch that forms the basis of digital circuits.Explained in How computers work
- Transit
- The passage of a planet in front of its star as seen from Earth.Explained in Exoplanets and the search for life
- Transpiration
- The release of water vapour from plant leaves.Explained in The water cycle
- Treaty of Versailles
- The 1919 peace treaty between the Allies and Germany.Explained in The First World War
- Tribune
- A Roman official empowered to veto measures against the interests of ordinary citizens.Explained in Greece and Rome: the political inheritance
- Tributary
- A smaller river or stream that flows into a larger one.Explained in Rivers and river systems
- Trilateration
- Finding a position from distances to several known points.Explained in How GPS works
- Triple Entente
- The informal alignment of France, Russia and Britain before 1914.Explained in The First World War
- Trophic cascade
- Effects of predators that spread down through several levels of a food web.Explained in Predators and prey
- Trophic level
- A feeding position in a food chain.Explained in Ecosystems: energy, matter and why food chains are short
U
- Urbanisation
- The movement of population from the countryside into towns and cities.Explained in The Industrial Revolution, Revolutions and the making of the modern state
- Utilitarianism
- The theory that the right act maximises overall happiness or wellbeing.Explained in Theories of ethics: consequences, duties and virtues
V
- Valence electrons
- Outermost-shell electrons, which determine bonding behaviour.Explained in Atoms and the periodic table
- Valid
- An argument in which the conclusion must be true if the premises are true.Explained in Logic and good reasoning
- Ventricle
- A lower chamber of the heart that pumps blood out.Explained in The heart and circulation
- Vernacular
- The everyday spoken language of a people, as opposed to Latin.Explained in The printing press and the information revolution
- Virus
- A particle of genetic material in a protein coat that replicates only inside cells.Explained in Viruses and bacteria
- VOC
- The Dutch East India Company, a powerful trading company founded in 1602.Explained in The spice trade
W
- Wadi
- A dry riverbed that fills with water only after rain.Explained in Deserts of the world
- Wavelength
- The distance between two matching points on successive waves.Explained in Waves, sound and light
- Weiqi
- The Chinese name for Go, a territory-surrounding game.Explained in The story of board games
- Work
- Energy transferred by a force moving its point of application.Explained in Energy, work and power
- Working memory
- The small, temporary store used to hold and manipulate information right now.Explained in How memory actually works
Y
- Yam
- The Mongol relay system of stations for messengers and official travellers.Explained in The Mongol Empire
- Yeast
- A single-celled fungus used to make bread, beer and wine.Explained in Fermentation: bread, cheese, yogurt and more
Z
- Zooxanthellae
- Symbiotic algae living inside coral tissue.Explained in Coral reefs