What is the generalization of a (2D) trapezoid/trapezium to 3D? I'm thinking of a convex polyhedron with 2 parallel faces, whose only other edges run between these 2 parallel faces. I.e., we have the convex hull of 2 parallel planar polygons, not necessarily congruent or similar, and not necessarily with the same number of sides. Is there a _name_ for such an object? (Hint: it _isn't_ a frustum, but some of the frustum formulae still work.)