rhombus

In geometry, a rhombus (or rhomb; plural rhombi) is a quadrilateral in which all of the sides are of equal length, i.e., it is an equilateral quadrangle. If any angle of an equilateral quadrangle is a right angle, then all its angles are right angles and it is also a square. In any rhombus opposite sides will be parallel. Thus, the rhombus is a special case of the parallelogram.