**Characterizations**

A simple (non self-intersecting) quadrilateral is a rhombus if and only if it is any one of the following:

- a quadrilateral with four sides of equal length (by definition)
- a quadrilateral in which the diagonals are perpendicular and bisect each other
- a quadrilateral in which each diagonal bisects two opposite interior angles
- a parallelogram in which at least two consecutive sides are equal in length
- a parallelogram in which the diagonals are perpendicular
- a parallelogram in which a diagonal bisects an interior angle

Read more about this topic: Rhombus