Cusp (singularity)
In the mathematical theory of singularities a cusp is a type of singular point of a curve. Cusps are local singularities in that they are not formed by self intersection points of the curve.
The plane curve cusps are all diffeomorphic to one of the following forms: x2 − y2k+1 = 0, where k ≥ 1 is an integer.
Read more about Cusp (singularity): More General Background, Examples