The portion of a surface left when an open disk is removed from it.
Perforation
See also
Open DiskExplore with Wolfram|Alpha
References
Francis, G. K. and Weeks, J. R. "Conway's ZIP Proof." Amer. Math. Monthly 106, 393-399, 1999.Referenced on Wolfram|Alpha
PerforationCite this as:
Weisstein, Eric W. "Perforation." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Perforation.html