Any of a variety of thermoplastics created from nitrocellulose and camphor, once used as photographic film.
1894 June, Antonia Dickson, W. K. L. Dickson, Edison's Invention of the Kineto-Phonograph: Account of the Invention, article in Century Magazine, Volume 48, Issue 2,
Then followed some experiments with drums, over which sheets of sensitized celluloid film were drawn, the edges being pressed into a narrow slot in the surface, similar in construction to the old tin-foil phonograph.
(figuratively, often used attributively) The genre of cinema; film.
(obsolete) An item, such as a jacket, made from celluloid.