A frame carrying film in a processing machine. Rack can also refer to frame edit alignment - where a projected film remains properly framed on screen (in rack). (Lab)
Rack Focus is a technique often used by video production services companies to shifting focus between subjects in the background and foreground so a viewer's attention moves from subject to subject as the focus shifts. Rack Focus can also be used for objects. It is often an effect which is used to create a dramatic or subtle change. (Camera crew)
When a different frame rate is used in the film production industry for example, to create slow motion, useful for filming sports video or live events. Shooting at a standard frame rate and then Ramping the frame rate to 75 fps will mean that the sports video or subject in a corporate video production will appear to be in slow motion when played back. (Film & video production)
