The omentum corresponds to two sheets of peritoneum joined together and which connect two viscera. It should not be confused with a ligament which corresponds to a joining of two sheets of peritoneum connecting the anterior parietal peritoneum to a viscera (e.g. the suspensory ligament of the liver), and with a meso which corresponds to a joining of two sheets of peritoneum connecting the posterior parietal peritoneum to a viscera and containing the feeder vessels (e.g. the mesentery of the small intestine)

• the greater omentum extends from the stomach to the transverse colon and forms a double-layered apron that is found on the surface of the intestines. The greater omentum is made up of the gastro-phrenic, gastro-splenic and gastrocolic ligaments.
• The lesser omentum is stretched from the stomach to the liver. It is composed of the gastrohepatic and hepatoduodenal (meso liver) ligaments.

Each omentum is crossed by numerous vessels.