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Browse key terms and definitions across all GCSE subjects. Search by keyword or filter by subject and exam board.
23,110 key terms
Exorcism
The casting out of an evil or unclean spirit believed to possess a person.
Exothermic
A reaction or change that transfers heat energy to the surroundings.
Exothermic
A process that releases energy to the surroundings. An exothermic chemical reaction has a negative overall energy change.
Exothermic change
A change that transfers energy from the reacting system to the surroundings, usually causing the measured mixture's temperature to rise.
Exothermic change
A change or reaction in which heat energy is given out to the surroundings.
Exothermic direction
A reaction direction that transfers energy from the reacting chemicals to the surroundings, usually by heating them.
Exothermic process
A chemical process that transfers energy from the reacting system to its surroundings.
Exothermic process
A process that transfers energy to the surroundings.
Exothermic reaction
A reaction that transfers energy to the surroundings.
Exothermic reaction
A reaction that transfers energy to the surroundings, leaving the products at a lower energy level than the reactants.
Exothermic reaction
A chemical reaction that transfers energy to its surroundings.
Expand
To multiply out brackets using the distributive law and then collect like terms.
Expanded plastic
A plastic containing many small gas-filled spaces, or cells, which reduce its density compared with the solid material.
Expanded polystyrene
A lightweight polystyrene foam made from expanded beads fused together, used for packaging and thermal insulation.
Expanding
Rewriting a product involving brackets as a sum or difference by multiplying out the brackets.
Expanding Universe
The large-scale increase in the distances between galaxies as space expands.
Expansion
Extending a state’s power into additional territories, for example through exploration, conquest and colonisation.
Expansion
Increasing the volume occupied by a gas.
Expansion
Rewriting a product containing brackets as a sum of terms by multiplying out the brackets.
Expansionism
A policy of extending a state’s territory or control beyond its existing boundaries.
Expansion of the Universe
The increase over time in the distances between widely separated galaxies as space expands.
Expectation
Hopes about the future; in Great Expectations, the word also refers to Pip’s anticipated receipt of property from a benefactor.
Expectation
A hope or belief about society or how people should behave.
Expectation
A belief about what is likely to happen or be encountered, based on previous experience or the current context.
Expectations
The prospect of receiving wealth or property in the future. Pip’s expectations also become entangled with his hopes of marrying Estella.
Expected frequency
The predicted number of occurrences of an event over repeated trials, calculated as probability multiplied by the number of trials.
Expected frequency
The number of occurrences predicted for an event over a stated number of trials, found from probability multiplied by the number of trials.
Expected frequency
The predicted number of times an event will occur, calculated as the number of trials multiplied by its theoretical probability.
Expected number
The expected number of occurrences is the probability of an event multiplied by the number of trials; it describes a long-run average, not a guaranteed count.
Expected output
The result a program should produce for a particular input, determined from its requirements before running the test.
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