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

(religion) The response of the congregation speaking alternately with the minister.

(phonology) Ablaut.

(linguistics) A pattern by which more than one construct is possible, as with "Alice cooked Bob dinner" and "Alice cooked dinner for Bob".

(logic) The "inclusive or" truth function.

(mathematics) A sequence that alternates between positive and negative values; sometimes incorrectly used to mean permutation.

(computing) A construct in a regular expression that can match any of several specified subexpressions.

(geometry) A type of partial truncation of a polygon, polyhedron or tiling in which alternate vertices are removed.