A cusp is a point at which two branches of a curve meet such that the tangents of each branch are equal. The above plot shows the semicubical
parabola curve 
,
which has a cusp at the origin.
Cusp
See also
Crunode, Double Point, Ordinary Double Point, Ramphoid Cusp, Salient Point, Semicubical Parabola, Spinode, TacnodeExplore with Wolfram|Alpha
References
Walker, R. J. Algebraic Curves. New York: Springer-Verlag, pp. 57-58, 1978.Referenced on Wolfram|Alpha
CuspCite this as:
Weisstein, Eric W. "Cusp." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Cusp.html