Lighting terms

Key light: The main source of light in a photograph of film
                  e.g. Sun, candle

Fill light: A supplementary light used in photography or filming that doesn't change the character of the main light and is used chiefly to lighten shadows
                   adding to the light

Backlight: Illumination from behind
                   separates the subject from the background shows importance/power/vulnerability 

Ambient (sets the scene)/Naturalistic (natural)/Artificial (fake)/Low key (not really standing out): Any source of light that isn't explicitly supplied by the photographer
                   sets the scene~Ambient

Chiaroscuro (Juxtaposition): An effect of contrasted light and shadow

Accent light/spotlight: A lamp projecting a narrow, intense beam of light directly onto a place or person, especially a performer on stage
                   focusses attention

Ambient and key light example

Backlight example