A & B Rolls:
Arranged for duplication, two or more matching rolls of film having alternate scenes intercut with opaque leaders in such a way that, from a common starting point, Roll "A" presents picture to the duplicate being printed where Roll "B" presents opaque leader, and vice-versa. This arrangement also permits double or multiple exposures in printing to obtain title or picture superimpositions, dissolves from one scene to another, and "checkerboarding" to eliminate the appearance of film splices on the screen. A third roll is called "C" roll, etc.
See also: