A rhombus is a parallelogram with four congruent sides. In other words, a rhombus is a quadrilateral with two pairs of parallel sides, all four of which have the same length. Rhombuses have some special properties that not all the parallelograms have. For instance, the diagonals of a rhombus bisect each other at a right angle. They also bisect the opposite angles. Rhombuses are symmetric about both diagonals. A rhombus with four right angles is called a square.