Refers to the body space between the thorax and pelvis.
The diaphragm forms the upper surface of the abdomen, while it ends at the level of the pelvic bones.
The abdomen ends where the pelvis begins.
It contains all the digestive organs, including the stomach, small and large intestines, pancreas, liver, and gallbladder, kidneys and spleen and the aorta, inferior vena cava, and dozens of vascular branches.
These organs are held together loosely by connective tissues, the mesentery.
Anteriorly it is protected by the fascia and posteriorly bounded by the back muscles.