The abdominal cavity is the part of the human body that is bounded superiorly by the diaphragm, inferiorly by the lesser pelvis, anteriorly by the muscles of the anterior abdominal wall and posteriorly by the vertebral column and muscles including Psoas and Quadratus lumborum.
It contains most of the gastrointestinal tract including the stomach, liver, gall bladder, pancreas, intestines (duodenum, jejunum, ileum, colon). The mouth, pharynx, oesophagus and a short section of rectum lie outside the abdominal cavity.
Also contained in the abdominal cavity are the left and right kidneys, the left and right ureters and the bladder.
In females, the abdominal cavity also contains the uterus, fallopian tubes and ovaries.
Altogether quite an important part of your body.