Polyhedron

A polyhedron is a three-dimensional geometric closed figure bounded by a connected set of polygons. A polyhedron, in Euclidian geometry, must have at least four faces. A polyhedron of four sides is called a tetrahedron, six sides a hexahedron, eight sides an octahedron, ten sides a decahedron. Figures with more sides are typically named with the Greek name for the number of sides, followed by "-hedron".

The polygons bounding a polyhedron are known as faces; the line segments bounding the polygons are known as edges, and the points where the faces meet are vertices (singular vertex).

A convex polyhedron bounded by faces which are all the same-sized regular polygon is known as a Platonic solid. There are only five Platonic solids, shown in the table below:

number of faces	name	type of face	properties	image
4	regular tetrahedron (or regular triangular pyramid)	equilateral triangle	4 vertices, 6 edges, self-dual
6	cube	square	8 vertices, 12 edges, dual to octahedron
8	regular octahedron	equilateral triangle	6 vertices, 12 edges, dual to cube
12	regular dodecahedron	regular pentagon	20 vertices, 30 edges, dual to icosahedron
20	regular icosahedron	equilateral triangle	12 vertices, 30 edges, dual to dodecahedron