Appendicitis is a condition in which the appendix becomes swollen, inflamed, and filled with pus. The appendix is a small pouch shaped like a small finger. It is on the right side of the abdomen, connected to the colon.Experts are not sure what the appendix is for. Charles Darwin wondered whether it might have been an organ our ancestors used to digest plants. Recent studies indicate that the appendix may be a dedicated environment for friendly bacteria which facilitate digestion and fight infection.Appendicitis generally affects people aged between 10 and 30, but it can strike at any age. Approximately 250,000 appendectomies are performed in the United States each year to treat appendicitis.