1. The part of the human body that contains all of the structures between the chest and the pelvis: The abdomen, or belly, is anatomically separated from the chest by the diaphragm, the powerful muscle that spans the body cavity, just below the lungs.
2. That section of the body that lies between the lower thorax or chest and the pelvis: The abdomen is the area of the body just below the diaphragm which contains the largest cavity in the body.

Also called belly (popular), venter, and stomach (incorrect). Derived from abdo, abdere, "to hide", and so probably originally referred to the "hidden part of the body".

Any belly condition with severe pain as a result of inflammation, perforation, obstruction, or injury of the stomach area: A medical term for the quick onset of abdominal pain, a potential medical emergency due to an acute abdomen, may reflect a major problem with one of the organs in the abdomen, such as appendicitis (inflamed appendix), cholecystitis (inflamed gallbladder), a perforated ulcer in the intestine, or a ruptured spleen, which is located on the left side of the abdomen near the stomach, filters blood, and serves as a major reservoir for blood.

A condition in which the excessively relaxed anterior, or front wall, of the abdomen hangs down over the pubis: Jack was getting tired of having a pendulous abdomen, involving weak abdominal wall muscles, so he decided to go to his doctor to ask for help!

Medical shorthand for a serious or severe abdominal pain; acute abdomen: A surgical abdomen may reflect a major problem or a potential medical emergency because of an alarming and dangerous situation of one of the organs in the abdomen.