A rectangle is a quadrilateral with two pairs of parallel sides and four equal angles (right angles (π∕2 rad) in Euclidean geometry (it can be less in hyperbolic geometry and can be more in spherical). It is a generalized example of a square because a rectangle all of the edges of a rectangle do not have to be equal in length. Another example of a generalized square is the rhombus, the rectangle's dual, because all of its angles do not have to be equal. A rectangle who has pairs of edges with different lengths is sometimes known as an oblong. Rectangles are parallelograms with four equal angles, parallelograms being quadrilaterals with two pairs of parallel sides that don't need right angles.
Rectangles are the cartesian product of two line segments, which don't need to be of equal length.