Note:  Do not rely on this information. It is very old.

Frustum

Frustum, in solid geometry, signifies that portion of a solid contained between any two planes of section. In the case of a, cone or other pyramid the base forms one plane of section, the other being taken anywhere between the base and the apex; the term is still further particularised, if no inclination of the second plane of section is mentioned, to refer to that portion between the base and any plane section parallel to the base. A frustum of a sphere or other conicoid similarly means the volume between any pair of parallel plane sections.