The belly or that part of the body that contains all of the structures between the chest and the pelvis: The abdomen is separated anatomically from the chest by the diaphragm, the powerful muscle spanning the body cavity below the lungs.

The part of the body below the thorax, containing the digestive organs and female reproductive organs: The abdomen is separated from the thorax by the diaphragm, a sheet of muscular tissue, while the "thorax" is the part of the human body between the neck and abdomen, enclosed by the ribs and containing the heart and lungs.

In anatomy, the third, posterior most major division of the body; belly, tummy: The abdomen is that part of a person's body between the thorax and the pelvis, but not including the back