- the act of alternating; occurrence, position, etc. of things by turns
- Linguis. the occurrence of a variant of a morpheme or phoneme
- The reciprocal succession of (normally two) things in time or place; the act of following and being followed by turns; alternate succession, performance, or occurrence; as, the alternation of day and night, cold and heat, summer and winter, hope and fear.
- The response of the congregation speaking alternately with the minister.
- (linguistics) Ablaut.
- (logic) The "inclusive or" truth function.
- (mathematics) A sequence that alternates between positive and negative values. (Sometimes wrongly used to mean a permutation.)
- (computing) A construct in a regular expression that can match any of several specified subexpressions.