An acute or chronic inflammation of the large intestine (the colon). There are many forms of colitis, including ulcerative, Crohns, infectious, pseudomembranous, and spastic. When inflammation becomes severe, cells are destroyed in the intestinal wall forming ulcers as exposure to the toxin or inflammatory byproducts continues. The ulcers bleed, and become infected often producing produce pus. Ulcerative colitis rarely affects the small intestine except for the lower section.