A film format is a technical definition of a set of standard characteristics regarding image capture on photographic film, for either stills or movies. It can also apply to projected film, either slides or movies. The primary characteristic of a film format is its size and shape.
Rollfilm or roll film is any type of spool-wound photographic film protected from white light exposure by a paper backing, as opposed to film which is protected from exposure and wound forward in a cartridge.
A silent film is a film with no synchronized recorded sound, especially spoken dialogue. In entertainment silent films the acting and dialogue is commuted through muted gestures, pantomime and title cards.
28 mm film was introduced by the Pathé Film Company in 1912 under the name Pathé Kok . Geared toward the home market, 28 mm utilized diacetate film stock rather than the flammable nitrate commonly used in 35 mm.