In algebra, the square of x is written x² and is defined as the product of x with itself: x × x. Taking the square is exponentiation with exponent two. If x is a positive real number, the value of x² is equal to the area of a (geometric) square of edge length x. If y = x² and x ≥ 0, then x is the square root of y.

A positive integer that is the square of some other integer is known as a square number, or more simply a square.