A polyhedron is a three-dimensional closed surface or solid, bounded by plane figures called polygons.

The word polyhedron comes from the Greek prefix poly-, which means "many," and the root word hedron which refers to "surface." A polyhedron is a solid whose boundaries consist of planes. Many common objects in the world around us are in the shape of polyhedrons. The cube is seen in everything from dice to clock-radios; CD cases, sticks of butter, or the World Trade Center towers are in the shape of polyhedrons called parallelpipeds. The pyramids are a type of polyhedron, as are geodesic domes. Most shapes formed in nature are irregular. In an interesting exception, however, crystals grow in mathematically perfect, and frequently complex, polyhedrons.

The bounding polygons of a polyhedron are called the faces. The line segments along which the faces meet are called the edges. The points at which the...