A dodecahedron is any polyhedron with twelve faces. In fact, the term is almost always used to refer specifically to a polyhedron with twelve pentagonal faces, and modifying words or alternate terminology are used to refer to other twelve-sided polyhedra, as in the case of the rhombic dodecahedron.
The regular dodecahedron is one of the five Platonic solids: its faces are all regular pentagons. It has twenty vertices and thirty edges. Three faces meet at each vertex. It is dual to the regular icosahedron. The dodecahedron is said to represent the universe; while the other four Platonic solids represent earth, fire, water and air, the five elements.