Rectouterine pouch: An extension of the peritoneal cavity between the rectum and back wall of the uterus. The term cul-de-sac, aside from being any blind pouch or cavity that is closed at one end, is used specifically to refer to the rectouterine pouch.ectouterine pouch: An extension of the peritoneal cavity between the rectum and back wall of the uterus. The term cul-de-sac, aside from being any blind pouch or cavity that is closed at one end, is used specifically to refer to the rectouterine pouch.