A point where a curve intersects itself along four arcs. The above plot shows the quadruple point at the origin
of the quadrifolium 
.
Quadruple Point
See also
Double Point, Triple PointExplore with Wolfram|Alpha
References
Walker, R. J. Algebraic Curves. New York:Springer-Verlag, pp. 57-58, 1978.Referenced on Wolfram|Alpha
Quadruple PointCite this as:
Weisstein, Eric W. "Quadruple Point." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/QuadruplePoint.html