Main Page | See live article | Alphabetical index In geometry, a rhombus is a quadrilateral in which all of the sides are of equal length. Opposite sides are parallel. The rhombus is a special case of the parallelogram, in that all sides are equal: the rhombus is to the parallelogram what the square is to the rectangle. If all the angles are right angles, it is then a square. The only plane figure that is both a rhombus and a rectangle is a square. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.