noun

1. 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

   "alternation between night shifts and day shifts"

2. The response of the congregation speaking alternately with the minister.

3. Ablaut.

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

   "dative alternation; locative alternation"

5. The "inclusive or" truth function.

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

7. A construct in a regular expression that can match any of several specified subexpressions.

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