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.