retroperitoneum
(REH-troh-PAYR-ih-toh-NEE-um)
The area in the back of the abdomen behind the peritoneum (the tissue that lines the abdominal wall and covers most of the organs in the abdomen). The organs in the retroperitoneum include the adrenal glands, aorta, kidneys, esophagus, ureters, pancreas, rectum, and parts of the stomach and colon.