In linguistics, alternation is the phenomenon where one phoneme is pronounced differently in different words. It occurs for grammatical, phonological and syntactical reasons. Each pronunciation is called an alternate.
The reciprocal succession of 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.
Alternation is the term used when a regular expression pattern chooses between two or more choices. For example, m/one|two|three/ will match if the string in contains any one of the three character sequences: one, two, or three. See also Regular Expression.