An obelisk is a stone pillar erected as a monument that usually consists of a pyramid atop a tall square (or sometimes rectangular base). The elongated
square pyramid can therefore be considered as a special case of an obelisk.

Harris and Stocker (1997) use the term "obelisk" to mean a polyhedron formed by two noncongruent parallel rectangles whose side faces are trapezoids. The volume
of such a solid is given by