Definition of Abdomen: WonderClub Dictionary

  The belly, or that part of the body between the thorax and
the pelvis. Also, the cavity of the belly, which is lined by the
peritoneum, and contains the stomach, bowels, and other viscera. In
man, often restricted to the part between the diaphragm and the
commencement of the pelvis, the remainder being called the pelvic
cavity.

  The posterior section of the body, behind the thorax, in
insects, crustaceans, and other Arthropoda.