The process of slowing the frame rate of a camera down, so that when the captured pictures are played at the normal frame rate the action appears to be in fast motion.
The opposite of slow-motion, it is also known as fast motion. Cinematographers refer to it as undercranking because it was originally achieved by cranking a hand-cranked camera slower than normal. It is often used for comic, or occasional stylistic effects. Extreme fast motion is known as time-lapse photography; a frame of, say, a growing plant is taken every few hours; when the frames are played back at normal speed, the plant is seen to grow before the viewer's eyes.