Ulcerative colitis (UC) is a condition which involves inflammation and ulceration of the lining of the large intestine, medically called as a colon. (Colitis= inflammation of colon). The inflammation related to ulcerative colitis usually occurs in the rectum and lower part of the colon, but it may affect the entire colon. Ulcerative colitis rarely affects the small intestine except for the lower section, called the ileum.