Diverticulosis is a condition in which there are small pouches or pockets in the wall or lining of any portion of the digestive tract. These pockets occur when the inner layer of the digestive tract pushes through weak spots in the outer layer. A single pouch is called a diverticulum. The pouches associated with diverticulosis are most often located in the lower part of the large intestine (the colon). Some people may have only several small pouches on the left side of the colon, while others may have involvement in most of the colon.