Generally, a face is a component polygon, polyhedron, or polytope. A two-dimensional face thus has vertices and edges, and can be used to make cells. More formally, a
face is the intersection of an 
-dimensional
polytope with a tangent hyperplane.
Zero-dimensional faces are known as polyhedron vertices
(nodes), one-dimensional faces as polyhedron edges,
-D faces as ridges,
and 
-dimensional faces as facets.
The illustration above illustrates the most commonly encountered face, namely that of a three-dimensional polyhedron.
