What is the meaning of Alternation?

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

The response of the congregation speaking alternately with the minister.

Ablaut.

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

The "inclusive or" truth function.

A sequence that alternates between positive and negative values.

A permutation.

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

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

Source: wiktionary.org