Likely to change or vary; subject to variation; changeable. Inconstant; fickle. Biology Tending to deviate, as from a normal or recognized type; aberrant. Mathematics Having no fixed quantitative value. Something that varies or is prone to variation. Astronomy A variable star. Mathematics A quantity capable of assuming any of a set of values. Mathematics A symbol representing such a quantity. For example, in the expression a2 + b2 = c2, a, b, and c are variables.