The pouch of Douglas, also known as the rectouterine pouch or rectovaginal pouch, is the extension of the peritoneum into the space between the posterior wall of the uterus and the rectum in females. It is the most dependent part of the peritoneal cavity when standing upright or lying supine. The pouch of Douglas represents the caudal extension of the peritoneal cavity and is an important site for peritoneal dialysis due to its deep location within the pelvis.