What is a frame rate?
Internet Filmmakers' FAQ
Frame Rate refers to the number of single "frames" of film that are exposed per second. Standard film is shot at 24 frames per second (fps). Prior to the 1930s, the standard frame rate for film was 18fps. This proved to be too slow for use with sync sound, hence the increase to today's standard rate.
It is possible to create time-based effects by adjusting the frame rate at which the film is shot and then playing it back at the standard 24fps. For slow-motion effects you increase your frame rate and thus the action is spread out over a longer piece of film. When this is played back at normal speed, the same action takes more time to progress, hence it is slower. For fast motion, the reverse is true. Indeed, the fact that old films were shot at 18fps is the reason why the action in many silent films tends to move a little faster than normal; when film which was shot at 18fps is played back at 24fps the action takes place 25% faster than it was in reality.
Frame rate is only applicable to film cameras, as video does not use frames in the same sense. Traditional video cameras operate in fields per second, in which two fields are displayed every second to produce one video "frame". This is also known as interlacing. For PAL, this effective frame rate is 25fps (or 50 fields per second), for NTSC the frame rate is 29.97fps (or 60 fields per second). Newer digital cameras sometimes use a recording mode known as 24p, which the camera records 24 video frames per second, but each frame is recorded progressively (hence the "p" notation) rather than in an interlaced fashion.