Abnormal side pockets in a hollow organ, such as the intestine:

The abnormal or unusual side pockets in a hollow organ, such as the intestine is called Diverticula.  A gut diverticulum is an outpouching of the wall of the gut to form a sac. It may occur at any level from aesophagus to colon. A true diverticulum includes all three layers of the gut; the lining mucosa, the muscularis, and the outer serosa; while the flase diverticula are missing the muscularis thus, they are thin walled.