arithmetic progression

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A sequence, such as the positive odd integers 1, 3, 5, 7, . . . , in which each term after the first is formed by adding a constant to the preceding term.

Wiktionary

1. n. analysis A sequence in which each term except the first is obtained from the previous by adding a constant value, known as the common difference of the arithmetic progression.

WordNet 3.0

1. n. (mathematics) a progression in which a constant is added to each term in order to obtain the next term