Some light sources, including mercury-vapor and fluorescent lamps, cycle on and off (flicker) at the same frequency as the AC current that powers them (generally 50 or 60 Hz). This flicker may appear during live view and movie recording and in recorded movies as cyclical bands wider than the “lines”. These bands are described as “horizontal bands” when they appear to be stationary.

The movie linked below shows “flicker” (horizontal bands moving rapidly in a vertical direction), while the effect of “horizontal bands” is shown by a still from the same movie.