Some properties of a rhombus are that its four sides are congruent, the opposite angles have equal measurements, the diagonals bisect each other and form 90 degrees at their intersection and the angles on an adjacent side are supplementary. Supplementary angles are two angles that add up to 180 degrees.
The formation of right angles at the intersection of the diagonals means that the diagonals are perpendicular. Some other properties pertaining to a rhombus are its perimeter and area formulas. The perimeter formula is 4 x the side length, and the area formula is (1/2) x C x D, where D and C are the diagonal lengths. The diagonals are not equal to each other.
A rhombus is a quadrilateral in which opposite sides are parallel. A square is a special case of a rhombus in which the angles are all equal to 90 degrees.