In photography, a graph that shows how increases in exposure increase the density of the film.

1. One of a pair of conjugate curves in a surface with the property that the directions of the tangents through any point of the curve are the characteristic directions of the surface.

2. A curve plotted on graph paper to show the relation between two changing values.

3. A characteristic curve of a one-parameter family of surfaces is the limit of the curve of intersection of two neighboring surfaces of the family as those surfaces approach coincidence.