The cavity of the body immediately inferior to the diaphragm is the cavity.

The cavity of the body immediately inferior to the diaphragm is the Abdominal cavity.

Explanation:

The body cavity is divided into upper thoracic cavity ad lower abdominal cavity. Both these cavities are separated by a membranous diaphragm. Above the diaphragm lies the Heart and a pair of lungs. Below the diaphragm in the abdominal cavity the following organs are present:

Liver, gall bladder, spleen, stomach, pancreas, small intestine, large intestine, and a pair of kidneys. The largest organ in the abdominal cavity is liver.

In the digestive system, rectum is a part of pelvic cavity which is below the abdominal cavity.

All the organs present inside are lined by a layer of peritoneum called visceral peritoneum whereas the abdominal wall is lined by parietal peritoneum.