A variable is a symbol that represents an unknown or changeable quantity, typically denoted by letters like x, y, or n.
Variables allow mathematical statements to be general and flexible. In expressions and equations, variables stand in for numbers that may be unknown or may vary. Independent variables are inputs (x), and dependent variables are outputs (y or f(x)). Variables are essential in algebra, calculus, statistics, programming, and all scientific modeling.
The modern use of letters as variables was pioneered by François Viète (16th century). René Descartes established the convention of using x, y, z for unknowns and a, b, c for constants.