A colostomy bag (or pouch) is worn on the outside of the body to collect waste that normally passes through the digestive system. The bag is needed after a portion of the colon has been surgically removed.
A person may need a colostomy bag temporarily until the colon has healed from the surgery. Or they may need the bag permanently if the entire lower part of the colon was removed. Solid waste passes from the remaining part of the colon through an opening (stoma) in the body. The bag doesn't show under clothing and is thrown away after each use. Many people are able to take care of their colostomy bags on their own.
WebMD Medical Reference from Healthwise