A rhombus is a parallelogram with four equal sides and opposite equal angles. A rhombus can be a square, or if it has two acute angles and two obtuse angles, it takes the shape of a diamond.
The rhombus gets its name from the Greek rhómbos, which means "a spinning top." This word describes the shape of a "bullroarer," an object that was tied to a cord and spun around, making a great noise. It was used to taunt bulls into action during bull-fighting events. This rhombus-shaped object has been documented as being used for religious rites and games all over the ancient world. Nowadays, we prefer to study the rhombus in geometry.