Great icosahedron.
Model and image courtesy Robert Webb

1. The process of constructing a new polyhedron
by extending the face planes of a given polyhedron past their edges. 2.
The new polyhedron thus obtained. Starting with the icosahedron,
for example, there are 59 possible stellations, including the great
icosahedron, which is one of the Kepler-Poinsot
polyhedra.