Glossary: Three-point lighting
A common arrangement within classical Hollywood cinema that uses three directions of illumination on a scene: from behind the subjects (backlighting), from one bright source (key light), and from a less bright source balancing the key light (fill light). The key light will usually be closer to the figure or brighter than the fill light. Typically, each major character in a scene will have his or her own key light, fill light, and backlight.
From Letter from an Unknown Woman
Frame 1: Three-point lighting (note that in this frame, Stefan, John, and the letter are each lit separately) Frame 2: Three-point lighting