Octahedron

In geometry, an octahedron (plural: octahedra) is a polyhedron with eight faces. A regular octahedron is a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex.

An octahedron is the three-dimensional case of the more general concept of a cross polytope.

Read more about Octahedron:  Dimensions, Orthogonal Projections, Cartesian Coordinates, Area and Volume, Geometric Relations, Related Polyhedra, Octahedra in The Physical World, Octahedra in Music, Other Octahedra, Tetrahedral Truss