A cel, short for celluloid, is a transparent sheet on which objects are drawn or painted for traditional, hand-drawn animation. Actual celluloid was used during the first half of the 20th century, but since it was flammable and dimensionally unstable it was largely replaced by cellulose acetate. With the advent of computer-assisted animation production, the use of cels has been all but abandoned in major productions. Disney studios stopped using cels in 1990 when Computer Animation Production System (CAPS) replaced this element in their animation process, and in the next decade and a half, the other major animation studios phased cels out as well.

Celluloids are a class of materials produced by mixing nitrocellulose and camphor, often with added dyes and other agents. Once much more common for its use as photographic film before the advent of safer methods, celluloid's common present-day uses are for manufacturing table tennis balls, musical instruments, combs, office equipment, fountain pen bodies, and guitar picks.