A figure with four equal sides and interior angles totaling 360 degrees is a square. A square is a regular quadrilateral: it has four straight sides of equal length and four right angles, with each angle measuring 90 degrees. Since 4 × 90° equals 360°, it fits the description exactly.
Squares belong to several shape families at once. Every square is both a rectangle, because it has four right angles, and a rhombus, because all four sides are equal. It is also a parallelogram, since opposite sides are parallel. However, not every rectangle or rhombus is a square.
The area of a square is found by multiplying its side length by itself, written as s². Its perimeter is four times the side length. The word “square” also became a mathematical verb because multiplying a number by itself mirrors the area calculation for a square.