addition

The operation, or process, of calculating the sum of two numbers or quantities.

absolute value

The distance a number is from zero on the number line. For example, -5 is 5 units away from zero. It would be written as |-5|.

acute angle

An angle whose measure is less than 90 degrees.

adjacent angles

Two angles that share a ray, thereby being directly next to each other.

affine cipher

Affine ciphers use linear functions to scramble the letters of secret mesages.

alternate exterior angles

Angles located outside a set of parallel lines and on opposite sides of the transversal.

alternate interior angles

Angles located inside a set of parallel lines and on opposite sides of the transversal.

angle bisector

A ray that divides an angle into two congruent angles.

area

The number of square units needed to cover a surface.

arithmetic mean

See mean.

average

It is better to avoid this sometimes vague term. It usually refers to the (arithmetic) mean, but it can also signify the median, the mode, the geometric mean, and weighted means, among other things.

average expected payoff

An estimate of the amount that will be gained in a game of chance, calculated by multiplying the probability of winning by the number of points won each time.

axioms of probability

There are three axioms of probability: 1. Probability is always more than zero 2. The chance that something happens is 1,or 100% 3. If two events cannot both occur at the same time, the chance that either one occurs is the sum of the chances that each occurs.