Variable (mathematics) definition

(1) (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"

(2) Liable to or capable of change

"Rainfall in the tropics is notoriously variable"

"Variable winds"

"Variable expenses"

(3) Marked by diversity or difference

"The varying angles of roof slope"

"Nature is infinitely variable"

(4) A quantity that can assume any of a set of values

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

(6) Something that is likely to vary; something that is subject to variation

"The weather is one variable to be considered"

(7) A star that varies noticeably in brightness