A double point at which two (or more) osculating curves are tangent. The above plot shows the
tacnode of the curve 
.
The capricornoid and links curve have tacnodes at their origins.
Tacnode
See also
Acnode, Capricornoid, Crunode, Double Point, Links Curve, Osculating Curves, SpinodeExplore with Wolfram|Alpha
References
Walker, R. J. Algebraic Curves. New York: Springer-Verlag, pp. 57-58, 1978.Referenced on Wolfram|Alpha
TacnodeCite this as:
Weisstein, Eric W. "Tacnode." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Tacnode.html