Plane geometric figure with four congruent sides and four right angles.

The term is also used to refer to a measure of area such as the square metre.

### Historical note

Originally, the term *“square”* referred to the geometric figure we still call a square. Greek mathematicians later used the term *“square”* to refer to the more abstract concept of a number \(c^{2}\) which represents the area of a square with side length *c* units.