A Variable

Something that is variable.
Something whose value may be dictated or discovered.
(mathematics) A quantity that may assume any one of a set of values.
(mathematics) A symbol representing a variable.
(programming) A named memory location in which a program can store intermediate results and from which it can read them.
(astronomy) A variable star.
(nautical) A shifting wind, or one that varies in force.
(nautical, in the plural) Those parts of the sea where a steady wind is not expected, especially the parts between the trade-wind belts.

(something that is variable): changeable
(something whose value may be dictated or discovered): parameter
(mathematics: a quantity that may assume any one of a set of values): variable quantity