A polyhedron
is a solid shape whose faces are all polygons. Polyhedra occur naturally
as the shapes of crystals, for example, alum, copper sulphate and
common salt.

A face is bounded by a circuit of edges, and is usually
a flat (plane) region called a polygon. The faces together make
up the polyhedral surface.

A polyhedron is a 3-dimensional example
of the more general polytope in any number of dimensions.

Example of a Polyhedron :