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Maths Glossary — A to Z
A plain English A–Z glossary of maths terms — from acute angle to volume. Search for any term to get a clear definition, perfect for checking understanding before exams.
A
- Acute angle
- An angle less than 90°.
- Adjacent
- Next to. In trigonometry, the side next to the angle (not the hypotenuse).
- Algebra
- The branch of maths using letters to represent unknown values.
- Arc
- Part of the circumference of a circle.
- Area
- The amount of space inside a 2D shape, measured in square units (cm², m²).
- Average
- A typical value for a data set. The three main averages are mean, median, and mode.
B
- Bearing
- A direction measured clockwise from north, written as a three-figure number (e.g. 045°).
- BODMAS
- Order of operations: Brackets, Order (powers), Division, Multiplication, Addition, Subtraction.
C
- Circumference
- The perimeter (distance around the outside) of a circle. C = 2πr.
- Coefficient
- The number in front of a variable in algebra. In 3x², the coefficient is 3.
- Common factor
- A number that divides exactly into two or more other numbers.
- Composite number
- A whole number greater than 1 that has more than two factors (i.e. not prime).
- Constant
- A fixed value that does not change.
- Coordinate
- A pair of numbers (x, y) giving a position on a grid.
D
- Denominator
- The bottom number of a fraction. In ¾, the denominator is 4.
- Diameter
- The distance across a circle through its centre. d = 2r.
- Difference
- The result of subtracting one number from another.
- Digit
- A single number symbol: 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9.
- Direct proportion
- When two quantities increase or decrease at the same rate. y = kx.
- Discriminant
- In the quadratic formula: b² − 4ac. Determines the number of real roots.
E
- Equation
- A mathematical statement that two expressions are equal.
- Equilateral triangle
- A triangle with all three sides equal and all angles 60°.
- Equivalent fractions
- Fractions that have the same value, e.g. 1/2 = 2/4 = 4/8.
- Expression
- A collection of terms and operations without an equals sign.
F
- Factor
- A whole number that divides exactly into another number.
- Frequency
- The number of times a value occurs in a data set.
- Function
- A rule that maps each input to exactly one output.
G
- Gradient
- The steepness of a line. Gradient = rise ÷ run.
- Graph
- A diagram showing the relationship between two quantities.
H
- HCF
- Highest Common Factor — the largest number that divides exactly into two or more numbers.
- Hypotenuse
- The longest side of a right-angled triangle, opposite the right angle.
I
- Index
- The power or exponent in an expression such as 2³. Also called an index number.
- Integer
- Any whole number, positive, negative, or zero.
- Interquartile range
- IQR = upper quartile − lower quartile. Measures spread of the middle 50%.
- Inverse proportion
- When one quantity increases as another decreases. xy = k (constant).
- Irrational number
- A number that cannot be written as a fraction. π and √2 are irrational.
- Isosceles triangle
- A triangle with two equal sides and two equal base angles.
L
- LCM
- Lowest Common Multiple — the smallest number that is a multiple of two or more numbers.
M
- Mean
- The average: sum of all values divided by the count.
- Median
- The middle value when data is arranged in order.
- Mode
- The most frequently occurring value in a data set.
- Multiple
- The result of multiplying a number by an integer. Multiples of 3: 3, 6, 9, 12...
N
- Numerator
- The top number of a fraction. In ¾, the numerator is 3.
O
- Obtuse angle
- An angle between 90° and 180°.
P
- Parabola
- The U-shaped curve formed by a quadratic function y = ax² + bx + c.
- Parallel
- Lines that are always the same distance apart and never meet.
- Perimeter
- The total distance around the outside of a 2D shape.
- Perpendicular
- Lines that meet at a right angle (90°).
- Pi (π)
- The ratio of a circle's circumference to its diameter. π ≈ 3.14159...
- Prime number
- A number with exactly two factors: 1 and itself. 2, 3, 5, 7, 11, 13...
- Probability
- The likelihood of an event, expressed as a value from 0 (impossible) to 1 (certain).
- Product
- The result of multiplying two or more numbers.
- Proportion
- A relationship between two quantities expressed as a ratio or fraction.
- Pythagoras' theorem
- In a right-angled triangle: a² + b² = c², where c is the hypotenuse.
Q
- Quadratic
- An expression or equation involving a squared term (x²) as the highest power.
- Quartile
- Values that divide an ordered data set into four equal parts.
- Quotient
- The result of dividing one number by another.
R
- Radius
- The distance from the centre of a circle to its edge. r = d ÷ 2.
- Range
- The difference between the largest and smallest values in a data set.
- Ratio
- A comparison of two or more quantities, written as a : b.
- Reciprocal
- The result of dividing 1 by a number. The reciprocal of ¾ is 4/3.
- Reflex angle
- An angle greater than 180° and less than 360°.
- Right angle
- An angle of exactly 90°, shown by a small square symbol.
S
- Scalene triangle
- A triangle where all three sides and all three angles are different.
- Sequence
- A list of numbers following a rule. E.g. 2, 5, 8, 11... (add 3 each time).
- Significant figures
- The meaningful digits in a number, starting from the first non-zero digit.
- Simplify
- To reduce a fraction or expression to its simplest form.
- Simultaneous equations
- Two or more equations with the same unknowns, solved together.
- SOHCAHTOA
- Memory aid for trigonometric ratios: Sin=Opp/Hyp, Cos=Adj/Hyp, Tan=Opp/Adj.
- Square number
- The result of multiplying an integer by itself. 1, 4, 9, 16, 25...
- Standard deviation
- A measure of how spread out the data is from the mean.
- Standard form
- A way of writing very large or small numbers: a × 10ⁿ, where 1 ≤ a < 10.
- Substitution
- Replacing a variable with a given numerical value.
- Sum
- The result of adding two or more numbers.
- Surd
- An irrational root that cannot be simplified to a whole number, e.g. √3.
T
- Tangent
- A straight line that touches a curve at exactly one point. Also tan in trigonometry.
- Term
- A single number, variable, or product in an expression or sequence.
- Trigonometry
- The study of relationships between sides and angles in triangles.
V
- Variable
- A letter representing an unknown or changing value in algebra.
- Vertex
- A corner or point where edges meet in a shape.
- Volume
- The amount of 3D space inside a solid shape, measured in cubic units (cm³, m³).
Frequently asked questions
What does "integer" mean in maths?+
An integer is any whole number — positive, negative, or zero. E.g., −3, 0, 5, 42 are all integers.
What is the difference between a factor and a multiple?+
A factor divides into a number exactly. A multiple is a number that can be divided by another number exactly.
What does "coefficient" mean?+
The coefficient is the number in front of a variable. In 3x, the coefficient of x is 3.
What is an irrational number?+
A number that cannot be written as a simple fraction. Examples: π and √2.