Polyhedron

+Some polyhedra120pxDodecahedron(Regular polyhedron)120pxSmall stellated dodecahedron(Regular star)120pxIcosidodecahedron(Uniform)120pxGreat cubicuboctahedron(Uniform star)120pxRhombic triacontahedron(Uniform dual)120pxElongated pentagonal cupola(Convex regular-faced)120pxOctagonal prism(Uniform prism)120pxSquare antiprism(Uniform antiprism)
A polyhedron (polyhedra or polyhedrons if more than one) is a geometrical shape. It is a 3D shape with flat faces, and straight edges. Each face is a polygon surrounded by edges. Usually it is known by the number of faces, corners, or edges it has. 

There are many groups of polyhedra, which can either be only a small set, or can be infinite. Prisms, pyramids, antiprisms, and bipyramids are groups of polyhedra. 

A regular polyhedron has faces that are all the same, corners that are all the same, and edges that are all the same. A uniform polyhedron can have one or two kinds of its parts be all the same. 

 Definition 
Two types of polyhedron are convex and concave. The edge connecting any two points of a convex polyhedron is inside the polyhedron. The line connecting two points of a concave polyhedron may go outside the polyhedron. The Platonic solids are regular convex polyhedra. 

Mathematicians do not always agree on what makes a polyhedron. Some may only consider the convex polyhedra, and disregard the ones that are not convex. Some polyhedra are degenerate, meaning that when drawn as real objects, they look flat.

 Naming 
Usually, polyhedra are named by the number of faces they have. The first polyhedra are the tetrahedron, which is made of four triangles, pentahedron (five faces, can look like a four-sided pyramid), hexahedron (six faces, a cube if it is regular), heptahedron (seven faces) and octahedron (eight faces). Prisms, pyramids and other shapes can also be named after how many faces they have.

 Other websites 

 Making Polyhedra
 Polyhedra Pages
 Stella: Polyhedron Navigator – Software for exploring polyhedra and printing nets for their physical construction.  Includes uniform polyhedra, stellations, compounds, Johnson solids, etc.
 The Uniform Polyhedra
 Virtual Reality Polyhedra – The Encyclopedia of Polyhedra
 Polyhedra and Pyramids
 Paper Models of Polyhedra Many links
 Paper Models of Uniform (and other) Polyhedra
 Interactive 3D  polyhedra in Java 
 World of Polyhedra  – Comprehensive polyhedra in flash applet, showing vertices and edges (but not shaded faces)
 Polyhedra software, die-cast models, and posters
 Electronic Geometry Models – Contains a peer reviewed selection of polyhedra with unusual properties
 Symmetry, Crystals and Polyhedra 
 uniform solution for uniform polyhedra by Dr. Zvi Har'El 
 Java applet with the use of kaleido 
 Origami Polyhedra – Models made with Modular Origami
 Polyhedra Collection – Various virtual and physical polyhedra models