Range of motion: The full movement potential of a joint, usually its range of flexion and extension. For example, a knee might lack 10 degrees of full extension due to an injury.
Range of motion (or ROM), is the linear or angular distance that a moving object may normally travel while properly attached to another. It is also called range of travel (or ROT), particularly when talking about mechanical devices and in mechanical engineering fields. For example, a sound volume control knob (a rotary fader) may have a 300° range of travel from the “off” or muted (fully attenuated) position at lower left, going clockwise to its maximum-loudness position at lower right.
As used in the biomedical and by weightlifters, range of motion refers to the distance and direction a joint can move between the flexed position and the extended position. The act of attempting to increase this distance through therapeutic exercises (range of motion therapy—stretching from flexion to extension for physiological gain) is also sometimes called range of motion.