A square has four right angles and four equal sides. It belongs to the set of polygons known as quadrilaterals, which are shapes with four sides.
A square is a special kind of rectangle. A rectangle is a quadrilateral that has four right angles and two pairs of equal opposite sides. Since the four sides of a rectangle are not required to be equal, all squares are rectangles, but not all rectangles are squares.
A square can also be classified as a rhombus. A rhombus is a quadrilateral with four equal sides and two pairs of equal opposite angles. However, since these angles are not required to be right angles, then all squares are rhombuses, but not all rhombuses are squares.