Stellation is a process of constructing new polygons (in two dimensions), new polyhedra in three dimensions, or, in general, new polytopes in n dimensions. The process consists of extending elements such as edges or face planes, usually in a symmetrical way, until they meet each other again. The new figure is a stellation of the original.
Read more about Stellation: Kepler's Definition, Stellated Polygons, Stellated Polyhedra, Stellated Polytopes, Naming Stellations, Stellation To Infinity