Polyhedron

Polyhedron, three-dimensional figure bounded by 4 or more polygon sides. There are only 5 types of convex polyhedron that can be regular (i.e., have faces that are equal regular polygons, each face being at equal angles to those adjacent to it); the tetrahedron, the octahedron, and the isocahedron, with 4, 8, and 20 faces, respectively, each face being an equilateral triangle; the hexahedron, with 6 square faces; and the dodecahedron, with 12 pentagonal faces. Regular polyhedrons may be circumscribed about or inscribed in a sphere.