the rhombus has a square as a special case, and is a special case of a kite
in plane euclidean geometry, a rhombus (plural rhombi or rhombuses) is a quadrilateral whose four sides all have the same length. another name is equilateral quadrilateral, since equilateral means that all of its sides are equal in length. the rhombus is often called a diamond, after the diamonds suit in playing cards which resembles the projection of an octahedral diamond, or a lozenge, though the former sometimes refers specifically to a rhombus with a 60° angle (see polyiamond), and the latter sometimes refers specifically to a rhombus with a 45° angle.
every rhombus is simple (non-self-intersecting), and is a special case of a parallelogram and a kite. a rhombus with right angles is a square.