Curves-on-surface are special curves that exist on a surface, and are used mostly for defining the line along which to trim the surface.

Curves-on-surface are special curves that are drawn in the UV space of a surface, rather than in the XYZ space of the scene. Curves-on-surface do not have CVs. They are controlled by moving on-curve edit points.

You can create curves-on-surface by drawing directly on the surface, by projecting existing curves onto a surface, and by intersecting existing geometry with a surface.

Curves-on-surface are usually used to trim surfaces, or to form the edge of new surfaces.