Three-point lighting

The three-point lighting is a standard method used in visual media such as video, film, still photography and computer-generated imagery. The technique uses three lights called the key light, fill light and back light.

Link to three-point lighting tutorial

Key-to-fill ratio
: ratio of the key light's intensity to the fill light's intensity

Low key-to-fill ratios (2:1 or less) may be used for

High key-to-fill ratios (8:1 or more) for

High/low key lighting
High key lighting is bright often shadowless scene in which the frame is predominantly lighter than medium gray. The environment has a lot of fill light and a low key-to-fill ratio. See the example below.

Low key lighting is a dark looking environment without much fill light, and a high key-to-fill ratio (film noir look). See the example below.

The images are from "Digital Lighting and Rendering" by Jeremy Birn.