A method of assembling alternate scenes of negative in A and B rolls allowing prints to be made without visible splices. 1
In film, an edited master of the original film material is assembled into two separate rolls, one for the odd numbered shots and one for the even numbered shots, so that dissolves, wipes and even supers can be overlapped and printed together, or hide splices on a print.
In video, there are two submaster tapes so that dissolves or wipes can be achieved from the two sources and recorded onto a third VTR.
References
1 Happe, L. B., 1983, Your Film and the Lab, 2nd Edition, Media Manuals, Focal Press, London, Boston