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Meaning of fast motion

fast' mo'tion

Pronunciation: [key]
— Cinematog.
  1. action that appears to move faster than normal on the screen, accomplished by filming the action at less than normal speed in the camera and then projecting it at normal speed. Cf. time-lapse photography.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.