The face poset of a convex polyhedron is
the set of all faces of
ordered by set inclusion.
Two polytopes are called isomorphic if
their face posets are isomorphic.
The face poset of a convex polytope is a lattice.
The face poset of a convex polyhedron is sometimes referred to as the combinatorial structure of the polyhedron. Thus the expression ``two polyhedra are combinatorially equal'' means they are isomorphic.