Polyhedron

A polyhedron is a three-dimensional solid that consists of a collection of polygons, joined at their edges.

Polyhedron is a high school-level concept that would be first encountered in a geometry course covering solid geometry.

Cube:	The cube is the Platonic solid comprised of six equal square faces that meet each other at right angles, eight vertices, and twelve edges.
Dodecahedron:	(1) A general dodecahedron is any polyhedron having 12 faces. (2) The regular dodecahedron is the Platonic solid comprised of 12 pentagonal faces, 20 vertices, and 30 edges.
Icosahedron:	(1) A general icosahedron is any polyhedron having 20 faces. (2) The regular icosahedron is the Platonic solid comprised of 20 equilateral triangles, 12 vertices, and 30 edges.
Octahedron:	(1) A general octahedron is any polyhedron having eight faces. (2) The regular octahedron is the Platonic solid comprised of eight equilateral triangular faces, eight edges, and six vertices.
Platonic Solid:	The Platonic solids are the five convex solids composed of identical regular polygons.
Pyramid:	A pyramid is a polyhedron with one face (known as the "base") a polygon and all the other faces' triangles meeting at a common polygon vertex (known as the "apex").
Tetrahedron:	(1) A general tetrahedron is any polyhedron having four faces. (2) The regular tetrahedron is the Platonic solid comprised of four equilateral triangles, four vertices, and six edges.