In geometry, a **rhombus** or **rhomb** is a quadrilateral whose four sides all have the same length. The rhombus is often called a diamond, after the diamonds suit in playing cards.

In general, a polygon whose sides have the same length is called equilateral, so a rhombus is an equilateral quadrilateral. Every rhombus is a parallelogram, and a rhombus with right angles is a square.

Its opposite angles are equal and they bisect each other at right angles.

The Rhombus diamond shape is used mainly in earrings and pendants or as side stones for rings which have been designed to accept the shape along the shank.