A polyhedron is a closed 3-D figure composed of some number of faces which are polygons. The simplest polyhedron is a tetrahedron composed of four triangles. Some polyhedra are regular; these have identical regular polygons for all their faces and the same dihedral angles at each edge, the same solid angles at each vertex. Euler's formula relates the number of faces, edges, and vertices in a polyhedron.
A stellated polyhedron can be formed from many normal polyhedra; this involves extending faces past their intersections to additional, more distant intersections.