Glossary
Every term a Grade 1–10, GCSE or SAT student meets, defined in one sentence.
The short answer
A working vocabulary for school mathematics, science, English and the exam system itself. Each entry gives one precise sentence a student can use, a worked example, and the point in the syllabus where the term first appears.
A
- Absolute valueThe absolute value of a number is its distance from zero on the number line, so it is never negative: |−7| and |7| are both 7.
- AccelerationAcceleration is the rate of change of velocity — the change in velocity divided by the time it takes — measured in metres per second squared.
- Active transportActive transport is the movement of substances across a cell membrane against the concentration gradient, using energy released by respiration.
- Adaptive testingAdaptive testing is computer-based testing in which the difficulty of later questions is chosen from how the candidate answered earlier ones, so two candidates sit different questions.
- Algebraic expressionAn algebraic expression is a combination of numbers, variables and operations with no equals sign, such as 3x + 2.
- AlleleAn allele is one of the different versions a gene can come in, sitting at the same place on a chromosome as the others.
- AlliterationAlliteration is the repetition of the same opening consonant sound in words that sit close together, judged by sound rather than by spelling.
- AmplitudeAmplitude is the maximum distance a point on a wave moves away from its undisturbed rest position.
- AnaphoraAnaphora is the deliberate repetition of the same opening words in a run of successive clauses, sentences or lines of verse.
- Angle of elevation and angle of depressionThe angle of elevation is the angle from the horizontal up to your line of sight; the angle of depression is the angle from the horizontal down to it.
- AntecedentAn antecedent is the noun or noun phrase that a pronoun refers to, so that the pronoun's meaning depends entirely on it.
- Arithmetic meanThe arithmetic mean is the total of a set of values divided by how many values there are.
- Arithmetic sequenceA sequence in which each term is found by adding the same fixed number, called the common difference, to the term before it.
- AsymptoteA straight line that a curve draws ever closer to as it runs out towards infinity, without ever meeting it.
- Atomic numberThe atomic number is the number of protons in the nucleus of an atom, and it determines which element that atom is.
- Axis of symmetryThe axis of symmetry of a parabola is the vertical line through its turning point, which reflects one half of the curve exactly onto the other.
B
- BiomeA biome is a large-scale region of the Earth defined by its climate and by the community of plants and animals that the climate supports.
- Box plotA box plot is a diagram of five values from a data set — the minimum, lower quartile, median, upper quartile and maximum — drawn against a single scale.
C
- CatalystA catalyst is a substance that speeds up a chemical reaction by lowering its activation energy and is not used up or chemically changed by the reaction.
- ChlorophyllChlorophyll is the green pigment inside chloroplasts that absorbs light energy, mostly red and blue, and makes that energy available for photosynthesis.
- ChordA chord is a straight line joining any two points on the circumference of a circle; the longest chord in a circle is its diameter.
- ChromatographyChromatography separates the substances in a mixture by how far each one travels through a stationary material while a moving solvent carries it along.
- ChromosomeA chromosome is one long, coiled molecule of DNA in the nucleus of a cell, carrying hundreds or thousands of genes along its length.
- ChronologyChronology is the ordering of events by the time at which they occurred, together with the system of dates used to fix them.
- CoefficientA coefficient is the number multiplying a variable in a term, such as the 5 in 5x².
- Common differenceThe fixed amount added to each term of an arithmetic sequence to get the next one, found by subtracting any term from the one that follows it.
- Common ratioThe fixed number each term of a geometric sequence is multiplied by to give the next one, found by dividing any term by the one before it.
- Composite functionA function formed by feeding the output of one function into another, written fg(x), which means apply g first and then f.
- Composite numberA composite number is a whole number greater than 1 with more than two factors, meaning it can be written as one smaller whole number multiplied by another.
- Concordance tableA concordance table pairs scores on two different tests that measure similar things, showing which score on one corresponds in standing to a given score on the other.
- Conditional probabilityConditional probability is the probability that one event happens given that another has already happened, calculated from the reduced set of outcomes still possible.
- CongruenceTwo shapes are congruent when they are the same shape and the same size, so one can be placed exactly on the other by turning, sliding or flipping it.
- Contour lineA contour line is a line on a map that joins all the points which are at the same height above sea level.
- Correlation and causationCorrelation is two quantities moving together in a pattern; causation is one of them making the other change, which correlation on its own can never establish.
- Correlation coefficientA correlation coefficient is a number between −1 and 1 saying how closely the points on a scatter graph lie to a straight line, and in which direction.
- CounterexampleA single example that satisfies a statement's conditions but not its conclusion, which is enough to prove the statement false.
- Cube rootThe cube root of a number is the value that gives that number when multiplied by itself three times; ∛64 = 4 because 4 × 4 × 4 = 64.
D
- Dangling modifierA dangling modifier is a descriptive phrase whose implied subject does not appear as the subject of the clause it is attached to.
- DenominatorThe denominator is the number below the line in a fraction, stating how many equal parts the whole has been divided into.
- DeterminerA determiner is a word placed in front of a noun to specify which one, whose, or how many are meant, such as the, this, my or several.
- Difference of two squaresAn expression made by subtracting one square from another, of the form a² − b², which always factorises into (a + b)(a − b).
- DiffusionDiffusion is the spreading out of particles from where they are crowded to where they are not, until they are evenly mixed.
- Discrete and continuous dataDiscrete data can only take separate fixed values that you count, while continuous data comes from measuring and can take any value within a range.
- DiscriminantThe part of the quadratic formula under the square root, b² − 4ac, whose sign tells you whether a quadratic has two real roots, one, or none.
- DistillationDistillation is a separation method in which a mixture is boiled and the vapour given off is cooled back into a liquid and collected apart from the rest.
- Domain of a functionThe set of input values a function is allowed to take — every x for which the rule produces a real answer.
- Dominant and recessive allelesA dominant allele shows its effect whenever it is present; a recessive allele shows only when both of an organism's alleles are recessive.
E
- Equilateral triangleAn equilateral triangle has three sides of equal length and three equal interior angles, each of which measures exactly 60 degrees.
- Error intervalAn error interval is the range of values a rounded or truncated measurement could have come from, written as an inequality between its lower and upper bounds.
- Exam boardAn exam board, or awarding body, is the organisation that publishes a specification, sets and marks the exam papers and issues the grade for a qualification.
- Exam seriesAn exam series is one scheduled window in which a board runs its papers, carrying a single timetable, one set of grade boundaries and one results day.
- Exothermic and endothermic reactionsAn exothermic reaction gives out energy and warms its surroundings; an endothermic reaction takes energy in and cools them.
- Expected frequencyExpected frequency is the number of times an outcome should occur on average, found by multiplying its probability by the number of trials.
- Exponential functionA function in which the variable appears as the power, written y = ka^x, so y is multiplied by the same factor each time x increases by one.
- ExtrapolationExtrapolation is estimating a value by continuing a pattern beyond the range of the data that was actually collected, which makes the estimate unreliable.
F
- ForeshadowingForeshadowing is a detail placed early in a story that hints at something happening later, so that the later event feels prepared for rather than sudden.
- FrequencyFrequency is the number of complete waves passing a fixed point each second, measured in hertz, where one hertz means one wave per second.
- Frequency densityFrequency density is the frequency of a class divided by its width, and it is the quantity plotted up the vertical axis of a histogram.
- Fronted adverbialA fronted adverbial is an adverbial moved from its usual position to the start of a sentence, where it is normally followed by a comma.
- FunctionA rule that assigns exactly one output to each input it accepts, so no input is ever sent to two different values.
G
- GenotypeA genotype is the pair of alleles an organism carries for a particular gene, usually written as two letters such as BB, Bb or bb.
- Geometric sequenceA sequence in which each term is found by multiplying the previous one by the same fixed number, called the common ratio.
- Grade boundaryA grade boundary is the lowest raw mark that earns a particular grade, fixed after marking so that the same grade represents the same standard across series.
- GradientA measure of how steep a line is, found by dividing the change in y by the change in x between any two points on it.
- Grading on a curveGrading on a curve means grades are set by how candidates rank against each other rather than against a fixed mark, so the same performance can earn different grades.
H
- HomeostasisHomeostasis is the way the body holds its internal conditions steady, such as temperature and blood glucose, while conditions outside it change.
- HyperboleHyperbole is deliberate exaggeration used for effect, stated as though it were literal but intended to be recognised as an overstatement.
- HypotenuseThe longest side of a right-angled triangle, the one lying directly opposite the right angle.
I
- Improper fractionAn improper fraction is one whose numerator is greater than or equal to its denominator, so its value is 1 or more — for example 7/4.
- Independent eventsTwo events are independent when the outcome of one has no effect on the probability of the other, so the probability of both equals the two probabilities multiplied.
- InferenceAn inference is a conclusion a reader reaches from evidence in a text about something the writer has implied but not stated directly.
- IntegerAn integer is any number in the list …, −3, −2, −1, 0, 1, 2, 3, … — a whole number, positive, negative or zero, with no fractional part.
- Interquartile rangeThe interquartile range is the upper quartile minus the lower quartile: the width of the middle half of an ordered data set.
- Inverse functionThe function that reverses another, sending each output of f back to the input it came from, and written f⁻¹.
- IonAn ion is an atom or group of atoms that has lost or gained electrons and therefore carries a positive or negative electrical charge.
- IronyIrony is a gap between appearance and reality: between what a speaker says and means, what is expected and what happens, or what a character knows and the audience knows.
- Irrational numberAn irrational number is a real number that cannot be written as a fraction of two integers, so its decimal runs on for ever without ever repeating.
- Isosceles triangleAn isosceles triangle has two sides of equal length, and the two angles opposite those equal sides are also equal to each other.
- IsotopeIsotopes are atoms of the same element with the same number of protons but different numbers of neutrons, and therefore different mass numbers.
K
L
- Like termsLike terms are terms whose letter parts are identical, including the powers, so they can be added or subtracted into one term.
- Linear equationAn equation in which every variable appears only to the power one, with no variables multiplied together, so its graph is a straight line.
- Linear qualificationA linear qualification is assessed entirely at the end of the course in one exam series, rather than in units taken and banked while the course is still running.
- LocusThe set of all points that satisfy a given rule about distance or position, drawn as the path or region those points form.
M
- Margin of errorThe margin of error is the amount added to and subtracted from a survey result to give the range in which the true population value plausibly lies.
- MeanderA meander is a bend in a river channel, maintained by erosion on the faster-flowing outer bank and deposition on the slower-flowing inner bank.
- MeiosisMeiosis is the cell division that makes gametes, dividing one cell twice to produce four genetically different cells with half the chromosome number.
- MetaphorA metaphor describes one thing as if it were another, transferring a quality from the second to the first without using like or as.
- MidpointThe midpoint of a line segment is the point exactly halfway between its two endpoints, found by averaging their x-coordinates and their y-coordinates.
- MitosisMitosis is the division of a cell nucleus that produces two daughter cells with identical DNA and the same chromosome number as the original.
- Mixed numberA mixed number is a whole number written next to a proper fraction, meaning the two added together — 2 3/4 means 2 + 3/4.
- Modal classThe modal class is the group in a grouped frequency table that contains more values than any other group.
- Modal verbA modal verb is a helping verb such as must, should or might that shows how certain, possible, permitted or obligatory the main verb's action is.
- ModerationModeration is an exam board's check on a school's marking of internally assessed work, shifting that school's whole cohort up or down if the marking proves too generous or severe.
- Mutually exclusive eventsTwo events are mutually exclusive if they cannot both happen at the same time, so on any single trial at most one of them occurs.
N
- Natural numberA natural number is one of the counting numbers — 1, 2, 3, 4 and onwards — though some conventions, including the standard ISO 80000-2, begin the list at 0.
- NetA net is a flat arrangement of a solid's faces, joined at their edges, that folds along those edges to form the solid without gaps or overlaps.
- NumeratorThe numerator is the number written on top of a fraction, and it counts how many of the equal parts are being taken.
O
- OnomatopoeiaOnomatopoeia is a word that imitates the sound it refers to, so that saying the word produces something close to the noise itself.
- OsmosisOsmosis is the net movement of water across a partially permeable membrane, from a dilute solution to a more concentrated one.
- OutlierAn outlier is a data value that lies far enough away from the rest of the data set to stand apart from it.
P
- Parallel linesLines in the same plane that stay the same distance apart for ever and so never meet, however far they are extended.
- Parallel structureParallel structure is the rule that words or phrases joined by and, or, or a paired conjunction must arrive in the same grammatical form as one another.
- ParallelogramA parallelogram is a quadrilateral with two pairs of parallel sides, which forces its opposite sides and opposite angles to be equal.
- Percentage multiplierA percentage multiplier is the single number an amount is multiplied by to apply a percentage change, such as 1.15 for a 15% increase.
- Percentage pointA percentage point is the difference between two percentages found by subtracting one from the other, as distinct from the percentage change between them.
- Percentile rankA percentile rank is the percentage of test takers in a stated comparison group who scored at or below a given score.
- PerpendicularTwo lines are perpendicular when they meet or cross at a right angle, exactly 90°.
- Perpendicular bisectorThe line that crosses a line segment at its midpoint at 90°, made up of every point that is the same distance from the segment's two ends.
- PersonificationPersonification describes a non-human thing as though it had human qualities or performed human actions, such as a wind that howls or a house that groans.
- PhenotypeA phenotype is the characteristic an organism actually shows, produced by its alleles together with the conditions it has grown in.
- PhonemeA phoneme is the smallest unit of sound in a spoken word: change one phoneme and the word changes, as pin becomes bin.
- Pi (π)Pi is the ratio of a circle's circumference to its diameter — approximately 3.14159, and identical for every circle regardless of size.
- Plan and elevationA plan is the view of a solid from directly above; an elevation is the view from directly in front of it or directly from one side.
- PolygonA closed two-dimensional shape made only of straight sides, each side meeting two others end to end.
- PolymerA polymer is a large molecule formed when many small molecules, called monomers, join together into a long repeating chain.
- Population and sampleThe population is every member of the group being studied; a sample is the smaller part of that group which is actually measured.
- Potential differencePotential difference is the energy transferred per coulomb of charge as it moves between two points in a circuit, measured in volts.
- Predicted gradeA predicted grade is a school's judgement, made before the exams, of the grade it expects a student to achieve — produced by teachers, never by the exam board.
- PressurePressure is the force acting at right angles to a surface divided by the area over which that force is spread, measured in pascals.
- Primary sourceA primary source is evidence created at the time of the event being studied, by someone who took part in it or witnessed it directly.
- PrismA prism is a solid whose cross-section is the same shape and size all the way along its length, with two identical parallel end faces.
- PropagandaPropaganda is information presented in a deliberately one-sided way in order to persuade an audience to hold a particular view or take a particular action.
- ProtagonistThe protagonist is the character whose goal drives the plot and around whose choices the story is organised, whether or not the reader is meant to approve.
- Pythagorean tripleA Pythagorean triple is a set of three positive whole numbers a, b and c for which a² + b² = c², so they form a right-angled triangle.
Q
- Quadratic sequenceA sequence whose second differences are all the same non-zero number, which means its nth term rule contains an n² term.
- QuadrilateralA quadrilateral is a flat shape with four straight sides and four corners, whose interior angles always add up to 360 degrees.
- Qualitative and quantitative dataQualitative data describes a quality in words or categories, while quantitative data records a quantity as a number that has been counted or measured.
- QuartileA quartile is one of the three values that split an ordered data set into four equally sized parts.
- QuotientThe quotient is the result of a division — the number of times the divisor goes into the dividend.
R
- RadianA radian is the angle at the centre of a circle that cuts off an arc equal in length to the radius.
- Random sampleA random sample is one chosen so that every member of the population has an equal chance of being selected.
- Range of a functionThe set of output values a function actually produces once every input in its domain has been used.
- Rational numberA rational number is any number that can be written as a fraction a/b where a and b are integers and b is not zero.
- ReciprocalThe reciprocal of a number is 1 divided by it — the number you multiply by to reach 1, found by turning a fraction upside down.
- Recurring decimalA recurring decimal is a decimal in which one digit or a block of digits repeats without end, shown by placing a dot over the repeating part.
- Reflex angleAn angle bigger than 180° but smaller than 360°: more than a straight line, less than a complete turn.
- RefractionRefraction is the bending of a wave as it passes from one material into another, caused by the change in the wave's speed at the boundary.
- Relative atomic massRelative atomic mass is the mean mass of an element's atoms, weighted by isotope abundance, compared with one twelfth of the mass of a carbon-12 atom.
- Relative clauseA relative clause is a subordinate clause that describes a noun, usually introduced by a relative pronoun such as who, which, that or whose.
- Relative frequencyRelative frequency is the number of times an outcome occurred divided by the total number of trials, used as an estimate of that outcome's probability.
- RemainderA remainder is the amount left over when one whole number does not divide exactly into another, and it is always smaller than the divisor.
- RhombusA rhombus is a quadrilateral with four sides of equal length whose opposite sides are parallel and whose diagonals cross at right angles.
- Rhyme schemeA rhyme scheme is the pattern made by the rhyming words at the ends of lines, recorded by giving each new rhyme sound the next letter of the alphabet.
- Roots of an equationThe values of the variable that make an equation true; for an equation written as f(x) = 0 they are exactly where the graph of f meets the x-axis.
S
- Sample spaceA sample space is the complete list of every possible outcome of an experiment, with each outcome written down exactly once.
- Sampling biasSampling bias is the error that arises when the way a sample is chosen makes some members of the population more likely to be included than others.
- Scalar and vector quantitiesA scalar is a quantity with magnitude only; a vector is a quantity that has both a magnitude and a direction, such as force or velocity.
- Scale factorA scale factor is the number by which every length in a shape is multiplied to produce an enlarged or reduced copy of the same shape.
- Scaled scoreA scaled score is a raw mark converted onto a fixed reporting scale, so that the same score means the same level of attainment whichever version was sat.
- SectorA sector is the region of a circle enclosed by two radii and the arc between their endpoints, like a slice cut from a whole pizza.
- SegmentA segment is the region of a circle cut off by a chord, lying between that chord and one of the two arcs the chord separates.
- SemicolonA semicolon is a punctuation mark that joins two closely related independent clauses, or separates list items that already contain commas.
- Significant figuresSignificant figures are the digits in a number that carry information about its size, counted from the first non-zero digit onwards.
- SimileA simile is a comparison between two unlike things, made openly with the word like or as, in order to give one of them a quality of the other.
- Simplest formA fraction is in simplest form when its numerator and denominator have no common factor other than 1, so no further cancelling is possible.
- Skewed distributionA skewed distribution is one whose graph is not symmetrical, having a longer tail stretching out on one side than on the other.
- Solute and solventA solute is a substance that dissolves in a liquid, the solvent is the liquid that dissolves it, and the mixture they form together is a solution.
- Specification codeA specification code is a short alphanumeric reference identifying one exact version of one qualification from one exam board, such as 1MA1 or 0580.
- Square numberA square number is what you get by multiplying an integer by itself, giving 1, 4, 9, 16, 25 and so on.
- Square rootA square root of a number is a value that gives that number when multiplied by itself; the sign √ denotes the positive one, so √25 = 5.
- Standard deviationStandard deviation is a measure of spread: roughly, how far a typical value sits from the mean of its data set.
- Stem-and-leaf diagramA stem-and-leaf diagram displays data in order by splitting each value into a stem, usually the leading digits, and a leaf, usually the final digit.
- StomataStomata are tiny pores in the surface of a leaf, mostly on the underside, that open and close to let gases in and out.
- Stratified sampleA stratified sample splits the population into groups and takes from each group a number of members in proportion to that group's size.
- Subject of a formulaThe subject of a formula is the single letter that stands alone on one side of the equals sign, with every other letter on the other side.
- Subordinate clauseA subordinate clause contains a subject and a verb but cannot form a sentence by itself; it depends on a main clause to complete its meaning.
- SurdA surd is a root of a rational number that is itself irrational, so it cannot be written exactly and is left in root form.
- Surface areaSurface area is the total area of all the faces and curved surfaces of a solid added together, measured in square units such as cm².
- SyllableA syllable is one beat of a spoken word, containing exactly one vowel sound, with or without consonants around it.
- SyntaxSyntax is the set of rules and choices governing how words are ordered and combined into phrases, clauses and sentences.
T
- Terminal velocityTerminal velocity is the constant speed reached by a falling object once the upward drag force acting on it has become equal in size to its downward weight.
- TessellationA tiling of a flat surface by shapes that fit together with no gaps and no overlaps, and which could continue for ever in every direction.
- Test-optionalTest-optional means a university considers an SAT or ACT score only if the applicant chooses to submit one, and does not penalise an application that arrives without one.
- The distributive propertyThe distributive property states that multiplying a sum gives the same result as multiplying each part separately and adding, so a(b + c) = ab + ac.
- Thesis statementA thesis statement is a single sentence stating the arguable claim an essay sets out to prove, placed early so a reader knows what is being argued.
- TieringTiering is the practice of examining one GCSE subject through two separate sets of papers, Foundation and Higher, each able to award only part of the grade range.
- Topic sentenceA topic sentence states the single point a paragraph will make, so that every sentence after it can be read as support for that point.
- TrapeziumA trapezium is a quadrilateral with one pair of parallel sides; the remaining two sides need be neither parallel, equal, nor at any particular angle.
- Triangular numberA triangular number is the total you get by adding the whole numbers from 1 up to some point, so that many dots can be arranged in an equal-sided triangle.
- Turning pointA point where a graph stops rising and begins to fall, or stops falling and begins to rise.
- Two-way tableA two-way table sorts one group of people or things by two different categories at once, showing how many fall into each combination.
U
V
W
- WavelengthWavelength is the distance between one point on a wave and the identical point on the next wave, such as from one crest to the next crest.
- WeatheringWeathering is the breaking down of rock in the place where it lies, by physical, chemical or biological processes, without the fragments being carried away.
X
Y
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