What is a fill light in stage theater?

In stage theater, a fill light is an additional light source (also referred to as footlights) placed on the floor in front of a performer or object to reduce the effect of shadows cast by overhead stage lights. These are generally warm lights.

By increasing the overall level of illumination on stage, fill lighting enables more uniform coverage, diminishes stark contrasts, softens the contours of objects and provides the actor's faces with a pleasing, three-dimensional look.