Range-of-motion exercises are exercises given to a patient following an injury, surgery, or procedure on a joint that may affect how well the joint can move.
The way you can move your shoulder, for example, provides you with and example of a range of motion. If you can move your arm in all the ways it is intended, you have a good range of motion. However, someone who has pain may not be able to move the arm as well. This is a restricted range of motion.
Physiotherapists provide ROM exercises to help enlarge that target range or to keep the current range from getting smaller.