A pillar is a landform, either of rock or earth, defined by the USGS as: "Vertical, standing, often spire-shaped, natural rock formation (chimney, monument, pinnacle, pohaku, rock tower)."^[1] Some examples of rock pillars are Chambers Pillar, Katskhi pillar, Pompeys Pillar, and Pillar Rock.

The Oxford Dictionary of Geography defines earth pillar as: "An upstanding, free column of soil that has been sheltered from erosion by a natural cap of stone on the top. They are common where boulder-rich moraines have been subject to gully erosion, as in parts of the southern Tyrol."^[2] A Hoodoo is another type of earth pillar. Examples of earth pillars are Awa Sand Pillars and Đavolja Varoš.