A conic section on which the midpoints of the sides of any complete quadrangle lie.
The three diagonal points 
, 
, and 
also lie on this conic.
Nine-Point Conic
See also
Complete Quadrangle, Conic Section, Diagonal Points, Nine-Point CircleExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Nine-Point Conic." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Nine-PointConic.html