The point of coincidence of 
and 
in Fagnano's theorem.
Fagnano's Point
See also
Fagnano's TheoremExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Fagnano's Point." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/FagnanosPoint.html