A rhombus is a parallelogram with four equal sides, like a square. Unlike a square, however, a rhombus has opposite and equal acute angles, and opposite equal obtuse angles — creating a diamond shape. It’s like a square that's leaning.
The rhombus gets its name from the Greek rhómbos, which means "a spinning top." This word comes from the shape of an object that was tied to a cord and spun around, making a great noise. This "bullroarer" 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 shape in geometry.