Time-lapse photography is a cinematography technique whereby the frequency at which film frames are captured (the frame rate) is much lower than that which will be used to play the sequence back. When replayed at normal speed, time appears to be moving faster and thus lapsing. For example, an image of a scene may be captured once every second, and then played back at 30 frames per second; the result would be an apparent increase of speed by 30 times. Time-lapse photography can be considered to be the opposite of high speed photography.
Processes that would normally appear subtle to the human eye, such as the motion of the sun and stars in the sky, become very pronounced. Time-lapse is the extreme version of the cinematography technique of undercranking, and can be confused with stop motion animation.
I tried to come up with an explanation that is both succinct and informative, but I think the wiki entry is the best for it.
I've always enjoyed such timelapse videos, and, to my eternal regret, I'm still not finding any good ones about the big US cities, like L.A. or New York. Nevertheless I think I have a few I'd like to share just because of how beautiful they are.The MountainThe MountainTime Elapse - Adagio in D minor http://youtu.be/cTRyZAI60DQ