A rhombus is an equilateral quadrilateral, which is a polygon having four sides of equal length.
A square is a special case of a rhombus where all four interior angles are ninety degrees.
In non-academic contexts, the term diamond can be applied to a rhombus, particularly if it is oriented with one of its diagonals vertical.
Its area is the product of its diagonals divided by two. Note that its diagonals are perpendicular to each other, and bisect each other.
In symbolic form, the area of a rhombus having diagonals of lengths D1 and D2 is:
This area also equals the length of a side (B) multiplied by the length of the perpendicular between two opposite sides (H):