variable

Likely to change or vary; subject to variation; changeable.

Inconstant; fickle.

Tending to exhibit genetic variation or variation in a physical trait.

Having no fixed quantitative value.

Something that varies or is prone to variation.

A variable star.

A quantity capable of assuming any of a set of values.

A symbol representing such a quantity. For example, in the expression a² + b² = c², a, b, and c are variables.