An obelisk is a form of monument from ancient Egyptian architecture, consisting of a slender, tapering, monolithic tower with a square plan rising to a pyramidal cap. While an obelisk should appear to be a solid shaft of rock, it can actually be hollow inside, and if large enough allow human entry.

The square plan, taper, and pointed cap determine the recognizable form. The solid appearance does not require the entire interior to be filled with stone.

A monumental column has a defined base, shaft, and capital. An obelisk instead ends in the pyramidal cap described above.