What is renvers and when is it used in dressage training?

Renvers — also called haunches-out or counter-travers — is the lateral movement that mirrors travers but with the relationship to the wall reversed: the horse's haunches remain on the track while its shoulders are brought slightly inward, with the horse bent away from the wall and in the direction of travel. In renvers on the right rein, the horse's outside shoulder is on or near the track, the inside shoulder is slightly off the track, and the horse is bent to the right — in the direction of travel — with the outside right hind stepping across toward the inside left front leg's track. Renvers is less commonly seen in training than shoulder-in or travers and is not required in any dressage test movement specifically, but it has valuable training applications as a suppling and strengthening exercise that works the horse's outside hind leg in a crossing and carrying pattern that the other lateral movements do not specifically demand. The outside hind leg in renvers must step across and under the body in a way that develops the outside hind's ability to carry — an important gymnastic preparation for pirouettes and other movements where the outside hind leg's engagement is critical. Renvers is also used as a suppling exercise for the horse's stiff side because it specifically demands lateral flexibility through the side of the horse that is on the outside of the bend, which for many horses is the stiffer side. Classical trainers include renvers in their programs primarily as a variation exercise — alternating between shoulder-in, travers, and renvers on the same track develops the horse's responsiveness and flexibility more completely than any single lateral movement can achieve — rather than as a primary movement that must be taught to a specific degree of refinement.