Generic term used in reference to any colored translucent material (color media) that is used to color a light, whether the material is made from gelatin, glass or plastic.
Coloured filters put over lights to give a coloured lighting effect. They used to be made out of gelatine.
Large coloured sheets of a transparent medium which are used over any type of light to add colour. (Also the smaller C.C. & camera filters.) (see CC filters)