A rectangle is a quadrilateral with four right angles.
- A parallelogram with at least one right angle
- A parallelogram with diagonals of equal length
- A parallelogram ABCD where triangles ABD and DCA are congruent
- An equiangular quadrilateral
- A quadrilateral with four right angles
- A quadrilateral where the two diagonals are equal in length and bisect each other