(1) The region of the body in between the thorax and the pelvis
(2) The part of the body where stomach, intestines, liver, spleen, and pancreas are contained inside a cavity lined by peritoneum
(3) (invertebrate biology) The posterior segment of invertebrates, after the thoracic segment
In vertebrates, such as humans, the abdomen contains visceral organs such as those of the digestive and urinary systems.
In humans, it is comprised of nine regions divided by two vertical and two horizontal lines :
In invertebrates, the abdomen generally pertains to the segment of their body after the thorax. It usually contains the digestive and reproductive structures.