AAS (Angle-Angle-Side)
A rule stating that two triangles are congruent if two angles and a non-included side of one are equal to the corresponding parts of the other.
Abacus
A counting tool with rows of beads that slide on rods, used for doing arithmetic.
Abscissa
The x-coordinate of a point on a coordinate plane.
Absolute maximum
The greatest value a function reaches over its entire domain.
Absolute minimum
The least value a function reaches over its entire domain.
Absolute value
The distance of a number from zero on a number line; always zero or positive.
Absolute value function
A function of the form f(x) = |x|, whose graph is V-shaped with its vertex at the origin.
Acre
A unit of area in the US customary system, equal to 43,560 square feet (about 4,047 square meters).
Acute angle
An angle whose measure is less than 90 degrees.
Acute triangle
A triangle that has three acute angles.
Addend
One of the numbers being added in an addition problem.
Addition
Finding the sum of two or more numbers.
Additive identity
The number zero, because adding zero to any number leaves the number unchanged.
Additive inverse
The opposite of a number; a number and its additive inverse add up to zero (for example, 5 and −5).
Adjacent angles
Two angles that share a common vertex and a common side but do not overlap.
Adjacent side (of a triangle)
In a right triangle, the leg that forms one side of a given acute angle (not the hypotenuse).
Algebra
The branch of mathematics that uses letters and symbols to represent numbers and quantities in formulas and equations.
Algebraic expression
A mathematical phrase that contains numbers, variables and operations, but no equals sign.
Algorithm
A step-by-step procedure for solving a problem or carrying out a calculation.
Alternate exterior angles
A pair of angles on opposite sides of a transversal and outside the two lines it crosses; they are equal when the lines are parallel.
Alternate interior angles
A pair of angles on opposite sides of a transversal and between the two lines it crosses; they are equal when the lines are parallel.
Altitude (of a triangle)
A perpendicular segment from a vertex of a figure to the opposite side or base; also called the height.
Amplitude
Half the distance between the maximum and minimum values of a periodic function, such as a sine or cosine wave.
Analog clock
A clock that shows time with an hour hand and a minute hand moving around a numbered dial.
Analytic geometry
The study of geometric figures using a coordinate system and algebra; also called coordinate geometry.
Angle
A figure formed by two rays that share a common endpoint, called the vertex.
Angle bisector
A ray or line that divides an angle into two equal angles.
Angle of depression
The angle between a horizontal line and the line of sight to an object below it.
Angle of elevation
The angle between a horizontal line and the line of sight to an object above it.
Annulus
The ring-shaped region between two circles that share the same center.
Antecedent
The "if" part of a conditional statement; also the first term of a ratio.
Antiderivative
A function whose derivative is the given function; also called an indefinite integral.
Apex
The highest point of a figure, such as the top vertex of a cone, pyramid or triangle.
Apothem
The perpendicular distance from the center of a regular polygon to one of its sides.
Approximation
A value that is close to, but not exactly equal to, the true value; often shown with the symbol ≈.
Arc
A part of the circumference of a circle between two points.
Arc length
The distance along the curve of an arc.
Arc measure
The measure of an arc in degrees, equal to the measure of its central angle.
Arccosine, Arcsine, Arctangent
The inverse trigonometric functions, which give the angle that has a given cosine, sine or tangent.
Area
The amount of space inside a two-dimensional figure, measured in square units.
Arithmetic
The branch of mathematics dealing with numbers and the basic operations of addition, subtraction, multiplication and division.
Arithmetic mean
The sum of a set of values divided by the number of values; the same as the average.
Arithmetic sequence
A sequence in which the difference between consecutive terms is always the same (for example, 3, 7, 11, 15…).
Arithmetic series
The sum of the terms of an arithmetic sequence.
Array
An arrangement of objects or numbers in equal rows and columns.
ASA (Angle-Side-Angle)
A rule stating that two triangles are congruent if two angles and the included side of one are equal to the corresponding parts of the other.
Ascending order
An arrangement of numbers or items from smallest to largest.
Associative property
The rule that the way numbers are grouped does not change the result of addition or multiplication: (a + b) + c = a + (b + c).
Asymmetry
The absence of symmetry; a figure is asymmetric if no line or point divides it into matching halves.
Asymptote
A line that a graph approaches more and more closely but never reaches.
Attribute
A characteristic of a shape or object, such as its number of sides, color or size.
Augmented matrix
A matrix that combines the coefficients and constants of a system of linear equations, used to solve the system.
Average
The number obtained by adding two or more quantities and dividing the sum by the number of quantities.
Average rate of change
The change in a function's output divided by the change in its input over an interval; the slope between two points.
Axiom
A statement accepted as true without proof, used as a starting point for reasoning; also called a postulate.
Axis
One of the reference lines in a coordinate system, such as the x-axis or y-axis.
Axis of symmetry
A line that divides a figure or graph into two mirror-image halves, such as the vertical line through the vertex of a parabola.