A frustum (unfortunately commonly misspelled "frustrum") is that portion of a solid which lies between two parallel planes cutting the solid. Degenerate cases are obtained for finite solids by cutting with a single plane only.
Frustum
See also
Conical Frustum, Pyramidal Frustum, Spherical SegmentExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Frustum." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Frustum.html