Adjoint Curve

A curve which has at least multiplicity $r_i-1$ at each point where a given curve (having only ordinary singular points and cusps) has a multiplicity $r_i$ is called the adjoint to the given curve. When the adjoint curve is of order $n-3$, it is called a special adjoint curve.

References

Coolidge, J. L. A Treatise on Algebraic Plane Curves. New York: Dover, p. 30, 1959.