A rhombus is actually just a special type of parallelogram. Recall that in a parallelogram each pair of opposite sides are equal in length. With a rhombus, all four sides are the same length.It therefore has all the properties of a parallelogram. See Definition of a parallelogram
Its a bit like a square that can 'lean over' and the interior angles need not be 90°. Sometimes called a 'diamond' or 'lozenge' shape.
| Base | Any side can be considered a base. Choose any one you like. If used to calculate the area (see below) the corresponding altitude must be used. In the figure above one of the four possible bases has been chosen. |
| Altitude | The altitude of a rhombus is the perpendicular distance from the base to the opposite side (which may have to be extended). In the figure above, the altitude corresponding to the base CD is shown. |
| Area | There are several ways to find the area of a rhombus. The most common is (base × altitude). Each is described in Area of a rhombus |
| Perimeter | Distance around the rhombus. The sum of its side lengths. See Perimeter of a rhombus |
| Diagonals | Each of the two diagonals is the perpendicular bisector of the other. See Diagonals of a rhombus |