The secondary or "safety" footage for non-narrative or interview based film. In order to string together two interview clips that were not shot consecutively, an editor will cut away from
A Roll to B Roll, while the audio from the A Roll shot plays under. Then when the editor cuts back to the second A Roll shot, it appears as if the concepts were always married together. This technique of using the
cutaway is common to hide zooms: the visuals may cut away to B roll footage of what the person is talking about while the A camera zooms in, then cut back after the zoom is complete. The cutaway to B roll footage can also be used to hide verbal or physical tics that the editor and/or director finds distracting: with the audio separate from the video, the filmmakers are freer to excise "uh"s, sniffs, coughs, and so forth.
/Talk