A set with a single point removed is called a punctured set, written .
Punctured Set
See also
Punctured PlaneExplore with Wolfram|Alpha
References
Krantz, S. G. Handbook of Complex Variables. Boston, MA: Birkhäuser, pp. 41-42, 1999.Referenced on Wolfram|Alpha
Punctured SetCite this as:
Weisstein, Eric W. "Punctured Set." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/PuncturedSet.html