A negative-height (inward-pointing) pyramid used in augmentation. The term was introduced by B. Grünbaum.
Invaginatum
See also
Augmentation, ElevatumExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Invaginatum." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Invaginatum.html