A polygon with four sides and four angles is called a quadrilateral. Quadrilaterals are two-dimensional, closed shapes with angle measurements that add up to 360 degrees.
Plane geometry recognizes five special kinds of quadrilaterals. Parallelograms consists of two pairs of parallel sides and have equal measurements for opposite sides and opposite angles. Squares are quadrilaterals in which all four sides and all four angles have equal measurements. Rectangles have four angles with equal measurements, and the opposite sides also have equal measurements. All squares are rectangles, but not all rectangles are squares. Trapezoids have exactly one pair of parallel sides. Rhombuses have four sides with equal measurements, and opposite pairs of sides are parallel. All rhombuses are parallelograms, but not all parallelograms are rhombuses. All squares are rhombuses, but not all rhombuses are squares.