Definition of "Variable" :

noun: a quantity that can assume any of a set of values

noun: a symbol (like x or y) that is used in mathematical or logical expressions to represent a variable quantity

noun: something that is likely to vary; something that is subject to variation

"The weather is one variable to be considered."

noun: a star that varies noticeably in brightness

adjective: (used of a device) designed so that a property (as e.g. light) can be varied

"A variable capacitor."

adjective: liable to or capable of change

"Rainfall in the tropics is notoriously variable."

adjective: marked by diversity or difference

"Nature is infinitely variable."