A cube is a three-dimensional solid, more properly called a polyhedron. It is made up of six congruent square faces all set at perpendicular angles. It is one of the five convex polyhedrons known as the Platonic solids.
The other Platonic solids are the tetrahedron, the octahedron, the dodecahedron and the icosahedron. These are the only convex polyhedrons made up entirely of congruent, regular polygonal faces. The faces of the dodecahedron are all regular pentagons, while the faces of the tetrahedron, octahedron and icosahedron are equilateral triangles. The Platonic solids are sometimes used as dice because their symmetry assures that there is an equal chance of the die landing on any face.