Mark a point 
on a side of a triangle and draw the perpendiculars
from the point to the two other sides. The line between the feet of these two perpendiculars
is called the pedal line.
Pedal Line
See also
Antipedal Line, Pedal Triangle, Simson LineExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Pedal Line." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/PedalLine.html