The solid bounded by plane polygons in space is called a polyhedron. Different polyhedrons are formed by different number of polygons. If a polyhedron is formed by a number of identical regular polygons, the same number of edges will converge at each vertex, and contiguous polygons will neighbor each other at he same angle. This kind of polyhedron is also called a regular polyhedron. There are five and only five types of regular polyhedrons, i.e., tetrahedrons, hexahedrons, octahedrons, dodecahedrons and icosahedrons. The ancient Greek philosopher Plato knew this in his era, so this is also called Plato-polyhedron.plato knew this in his era so this is also called plato-polyhedron.