This term refers to the physical size or dimensions of the film, as film generally has a set amount of resolution or information it can record per square cm, the larger the film the more information that can be recorded. Although film use has diminished considersably, standard film sizes in use today are 35mm, 120, 4x5inches and 8x10 inches.

This is similar in digital cameras, the larger the ccd the more information that can be recorded.