hermit point

An acnode, also called an isolated point or hermit point, of a curve is a point that satisfies the equation of the curve but has no neighboring points that also lie on the curve. The plot above shows the curve y^2 + x^2 + x^3 = 0, which has an acnode at the origin (0, 0). The conchoid of de Sluze has an acnode at the origin for a>-1.

crunode | cusp | singular point | spinode | tacnode