extension [ek-sten´shun] 1. the movement by which the two ends of any jointed part are drawn away from each other. 2. a movement bringing the members of a limb into or toward a straight condition.

Extension is a type of body movement in anatomy and physiology that increases the angle between two parts at a joint, typically straightening from a flexed position.

extension noun ex·​ten·​sion ik-ˈsten-chən 1 : the stretching of a fractured or dislocated limb so as to restore it to its natural position 2 : an unbending movement around a joint in a limb (as the knee or elbow) that increases the angle between the bones of the limb at the joint compare flexion sense 1