1) Theatrical color filter used in conjunction with theatrical projection fixtures and spotlights. 2) Gelatin.
Colored material placed in front of a light source to alter its hue. Useful for correcting mismatches in lighting, as in scenes lit by both daylight and artificial light.
coloured filter, used to change the colour of light from a lantern. Originally made from gelatin (hence the name), nowadays gels are made of dyed polyester film. Also known as colour.