A geometric solid is a portion of space which is completely enclosed, or separated from the rest of space, by some type of surface. The threedimensional figures with polygon faces are categorized as polyhedra.

A polyhedron (plural polyhedra) is a threedimensional solid with flat polygon faces joined at their edges. 
The word polyhedron is derived from the Greek poly meaning "many",
and the IndoEuropean hedron meaning "seat or face".
A polyhedron's faces are bounding surfaces consisting of portions of intersecting planes. 

A polyhedron has no curved surfaces.
The "faces" (sides) are flat, plane surfaces.
We will be working with polyhedra that are referred to as prisms and pyramids:
In the polyhedra shown above, the sides of the figures are not all of the same shape or size.
If all of the sides are the same shape and size, the figure is called a regular polyhedron.
The regular polyhedra that we will be seeing are a triangular pyramid whose sides are all equilateral triangles, and a cube (a square prism) whose sides are all squares.
There are a total of five such regular polyhedra called the Platonic Solids,
after the ancient Greek philosopher Plato, in whose writings they first appeared.
The Platonic Solids
Tetrahedron 
Octahedron 
Icosahedron 
Cube 
Dodecahedron 





The cube is also called a hexahedron.
While there is no limit to the number of regular twodimensional polygons,
there is a limit to the number of regular polyhedra! There are only five!
We will also be dealing with 3D shapes that are NOT polyhedra:
These solids are not polyhedra since a part, or all, of the figure is curved.