A rhombus has exactly four sides and has a diamond shape. All the sides of a rhombus are the same length, and its opposite sides are parallel to each other. The difference between a rhombus and a square is that the angles in a rhombus cannot be 90 degrees.
The area of a rhombus can be calculated similarly to the area of a square or rectangle. The length of one side is multiplied by the altitude to calculate the shape's area. The altitude is the distance of a perpendicular line from one of the sides to the its opposite side.