A diamond is a two-dimensional flat quadrilateral having four straight sides that are closed. A diamond is also known as a rhombus because its sides are equal in length and the interior opposing angles are equal. Outside of the arithmetic classroom, diamond forms may be discovered. A diamond is a useful object for displaying items such as jewelry or trophies. In mathematics, the term "diamond" refers to any one of several figures with these properties: they have exactly four sides, each side is parallel to at least one other side, and each angle is 90 degrees (or 180 degrees if you count both directions as separate angles). Such figures include rectangles, squares, and triangles with four right angles; more generally, any polygon with exactly four vertices can be considered a diamond. In geometry, a diamond is a figure consisting of four equidistant lines meeting at a point. The word "diamond" may also be used as an adjective to describe such figures: a square diamond, a rectangular diamond, etc. The term "diamond shape" is also used to describe various figures that are not necessarily polygons. These include circles, ellipses, and hyperbolas with four focal points. Also included are parabolas whose axes of symmetry cross at right angles, such as the one shown on the left in red.