In geometry, a parallelepiped is a three-dimensional figure formed by six parallelograms (the term rhomboid is also sometimes used with this meaning). By analogy, it relates to a parallelogram just as a cube relates to a square or as a cuboid to a rectangle. In Euclidean geometry, its definition encompasses all four concepts (i.e., "parallelepiped", "parallelogram", "cube", and "square"). In this context of affine geometry, in which angles are not differentiated, its definition admits only "parallelograms" and "parallelepipeds". Three equivalent definitions of "parallelepiped" are