Tetrahedron

• In geometry, a tetrahedron is a polyhedron composed of “four triangular faces”three of which meet at each vertex

• A regular tetrahedron is one in which the four triangles are regular, or "equilateral", and is one of the Platonic solids.

• The tetrahedron is the only convex polyhedron that has four faces. The tetrahedron is one kind of pyramid.

TetrahedronNet View

• In geometry the net of a polyhedron is an arrangement of edge-joined polygons in the plane which can be folded (along edges) to become the faces of the polyhedron.

TetrahedronVertex View

• In geometry a vertex figure is, broadly speaking, the figure exposed when a corner of a polyhedron or polytope is sliced off.

Sources

http://en.wikipedia.org/wiki/Tetrahedron