Definition of variable:
something that is likely to vary; something that is subject to variation; "the weather is one variable to be considered"
a quantity that can assume any of a set of values
a star that varies noticeably in brightness
a symbol (like x or y) that is used in mathematical or logical expressions to represent a variable quantity
liable to or capable of change; "rainfall in the tropics is notoriously variable"; "variable winds"; "variable expenses"
marked by diversity or difference; "the varying angles of roof slope"; "nature is infinitely variable"
(used of a device) designed so that a property (as e.g. light) can be varied; "a variable capacitor"; "variable filters in front of the mercury xenon lights"