From AMS Glossary
- (Also called mean, average, simple average.) One of several accepted measures of central tendency, physically analogous to "center of gravity."
Pertaining to a set of numbers x1, x2, . . ., xn, the arithmetic mean, usually denoted by the symbol, is the sum x1 + x2 + . . . + xn divided by n. Since the word "mean" is also applied to other measures of central tendency, such as weighted means, geometric means, and harmonic means, the adjective "arithmetic" is used for clarity. However, when used without further qualification, the term "mean" is understood as arithmetic mean.
Compare geometric mean.