Capacity
The amount a container can hold when full, measured in units such as liters, milliliters, cups or gallons.
Cardinal number
A number that tells how many things are in a set, such as 1, 2, 3 or 5.
Cartesian plane
A flat surface formed by a horizontal x-axis and a vertical y-axis that cross at the origin, used to locate points; also called the coordinate plane.
Celsius
A temperature scale on which water freezes at 0° and boils at 100° at sea level.
Center
The point that is the same distance from every point on a circle or sphere, or the middle point of a figure.
Centimeter
A metric unit of length equal to one hundredth of a meter, about the width of a large paper clip.
Central angle
An angle whose vertex is at the center of a circle and whose sides are radii.
Centroid
The point where the three medians of a triangle meet; the triangle's balance point.
Century
A period of 100 years.
Chain rule
A rule for differentiating a composite function: the derivative of f(g(x)) is f′(g(x)) times g′(x).
Change of base formula
A formula that rewrites a logarithm in another base: log_b a = log a ÷ log b.
Chord
A line segment whose endpoints both lie on a circle. The longest chord is the diameter.
Circle
A plane figure made of all points that are the same distance (the radius) from a fixed point (the center).
Circle graph
A graph that shows parts of a whole as sectors of a circle; also called a pie chart.
Circumcenter
The point where the perpendicular bisectors of a triangle's sides meet. It is the center of the circle that passes through all three vertices.
Circumference
The distance around a circle, found with C = 2πr or C = πd.
Circumscribed
Drawn around a figure so that it touches every vertex, such as a circle drawn around a square.
Clockwise
Turning in the same direction as the hands of a clock.
Closed interval
An interval that includes both of its endpoints, written with square brackets, such as [2, 5].
Coefficient
The number multiplied by a variable in a term. In 7x², the coefficient is 7.
Collinear
Points that lie on the same straight line.
Column
A vertical arrangement of items, such as numbers in a table, matrix or array.
Combination
A selection of items where order does not matter. Choosing 2 letters from A, B and C gives 3 combinations: AB, AC and BC.
Commission
Money paid to a salesperson, usually a percent of the total sales they make.
Common denominator
A number that is a multiple of the denominators of two or more fractions, so the fractions can be added, subtracted or compared.
Common difference
The amount added to each term to get the next term in an arithmetic sequence.
Common factor
A number that divides evenly into two or more numbers. The common factors of 12 and 18 are 1, 2, 3 and 6.
Common logarithm
A logarithm with base 10, usually written without the base: log 1000 = 3 because 10³ = 1000.
Common multiple
A number that is a multiple of two or more numbers. 12 and 24 are common multiples of 4 and 6.
Common ratio
The number each term is multiplied by to get the next term in a geometric sequence.
Commutative property
The rule that changing the order of numbers does not change the result of addition or multiplication: a + b = b + a.
Comparison
Deciding whether one number or quantity is greater than, less than or equal to another, using the symbols >, < or =.
Compass
A tool with two hinged legs, one with a point and one with a pencil, used to draw circles and arcs.
Compatible numbers
Numbers that are easy to compute with mentally, used to estimate an answer.
Complement (of an event)
All outcomes in which an event does not happen. Its probability is 1 minus the probability of the event.
Complementary angles
Two angles whose measures add up to 90 degrees.
Completing the square
A method of rewriting a quadratic such as x² + 6x as a perfect square, (x + 3)² − 9, by adding the missing constant.
Complex fraction
A fraction whose numerator, denominator or both contain a fraction.
Complex number
A number of the form a + bi, where a and b are real numbers and i is the square root of −1.
Composite figure
A figure made of two or more simpler shapes. Its area is the sum of the areas of the parts.
Composite number
A whole number greater than 1 that has more than two factors. 12 is composite because it has factors 1, 2, 3, 4, 6 and 12.
Composition of functions
Applying one function to the result of another, written f(g(x)) or (f ∘ g)(x).
Compound event
An event made up of two or more simple events, such as flipping heads and rolling a 6.
Compound inequality
Two inequalities joined by "and" or "or", such as −2 < x ≤ 3.
Compound interest
Interest earned on both the original amount and on interest already earned, given by A = P(1 + r)ᵗ.
Concave polygon
A polygon with at least one interior angle greater than 180°, so part of it caves inward.
Concentric circles
Two or more circles that share the same center.
Conditional probability
The probability that an event happens given that another event has already happened, written P(A | B).
Conditional statement
A statement in "if p, then q" form, written p → q.
Cone
A solid figure with a circular base connected to a single point called the vertex (or apex).
Congruent
Having exactly the same size and shape. The symbol is ≅.
Conic sections
The curves formed when a plane cuts a double cone: circle, ellipse, parabola and hyperbola.
Conjecture
A statement believed to be true based on a pattern or observations, but not yet proven.
Conjugate
A binomial formed by changing the sign between the two terms. The conjugate of 3 + √2 is 3 − √2.
Consecutive interior angles
Two angles between two lines on the same side of a transversal. When the lines are parallel, they add up to 180°; also called same-side interior angles.
Consecutive numbers
Numbers that follow one another in order without gaps, such as 5, 6, 7, 8.
Constant
A value that does not change. In 3x + 7, the constant term is 7.
Constant of proportionality
The constant ratio k between two proportional quantities, as in y = kx.
Continuous data
Data that can take any value in a range, such as height, time or temperature, rather than only separate counts.
Contrapositive
The statement formed by reversing and negating both parts of a conditional. The contrapositive of "if p, then q" is "if not q, then not p".
Converse
The statement formed by swapping the two parts of a conditional. The converse of "if p, then q" is "if q, then p".
Conversion
Changing a measurement from one unit to another, such as meters to centimeters.
Conversion factor
A ratio equal to 1, such as 12 in / 1 ft, that you multiply by to change units.
Convex polygon
A polygon in which every interior angle is less than 180°, so no part caves inward.
Coordinates
An ordered pair of numbers, such as (3, 2), that gives the position of a point on a graph.
Coplanar
Points or lines that lie in the same plane.
Coprime
Two numbers whose only common factor is 1, such as 8 and 15; also called relatively prime.
Correlation
A relationship between two variables in which they tend to change together. It can be positive, negative or none.
Corresponding angles
Angles in matching positions where a transversal crosses two lines. When the lines are parallel, corresponding angles are equal.
Corresponding sides
Sides in matching positions on two congruent or similar figures.
Cosecant and cotangent
Two reciprocal trigonometric functions: csc θ = 1 / sin θ and cot θ = 1 / tan θ.
Cosine
In a right triangle, the ratio of the side adjacent to an angle to the hypotenuse: cos θ = adjacent / hypotenuse.
Coterminal angles
Angles in standard position that share the same terminal side, such as 30° and 390°.
Counterclockwise
Turning in the opposite direction to the hands of a clock.
Counterexample
A single example that shows a general statement is false.
Counting numbers
The numbers 1, 2, 3, 4 and so on, used for counting; also called natural numbers.
CPCTC
Short for "corresponding parts of congruent triangles are congruent". Once two triangles are proven congruent, all their matching sides and angles are equal.
Cross products
In a proportion a/b = c/d, the products ad and bc. They are equal when the proportion is true, which is how cross multiplication works.
Cross section
The shape you see when a plane cuts through a solid figure.
Cube
A solid figure with six square faces, all the same size.
Cube root
A number that, multiplied by itself three times, gives the original number. The cube root of 27 is 3.
Cubic unit
A cube with edges one unit long, used to measure volume, such as 1 cm³.
Cuboid
A solid figure with six rectangular faces; also called a rectangular prism.
Cumulative frequency
The running total of frequencies up to each value or class in a data set.
Currency
The money used in a country, such as dollars, euros or kroner.
Cylinder
A solid figure with two congruent, parallel circular bases joined by a curved surface.