Range of motion

range within with a joint can be flexed and extended (measured in degrees), ROM

Range of motion or (ROM), as used in the biomedical and weightlifting communities, is the measurement of the achievable distance between the flexed position and the extended position of a particular joint or muscle group. 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.
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Range of motion The range of motion of a joint from full extension to full flexion measured in degrees like a circle. [more]Range of motion - Community and Resources

The range through which a joint can be moved, usually its range of flexion and extension. Due to an injury, the knee may for example lack 10 degrees of full extension.