The human abdomen (from the Latin word meaning "belly") is the part of the body between the pelvis and the thorax. Anatomically, the abdomen stretches from the thorax at the thoracic diaphragm to the pelvis at the pelvic brim. The pelvic brim stretches from the lumbosacral angle (the intervertebral disk between L5 and S1) to the pubic symphysis and is the edge of the pelvic inlet. The space above this inlet and under the thoracic diaphragm is termed the abdominal cavity. The boundary of the abdominal cavity is the abdominal wall in the front and the peritoneal surface at the rear.

Functionally, the human abdomen is where most of the alimentary tract is placed and so most of the absorption and digestion of food occurs here. The alimentary tract in the abdomen consists of the lower oesophagus, the stomach, the duodenum, the jejunum, ileum, the cecum and the appendix, the ascending, transverse and descending colons, the sigmoid colon and the rectum. Other vital organs inside the abdomen include the liver, the kidneys, the pancreas and the spleen.