Appendix comes from the Latin appendere, meaning to "hang from". The most familiar appendix in the body is the vermiform ("worm-like") appendix which is attached to the the cecum of the large intestine. It contains lymphatic tissue and thus plays a role in immune function, albeit a very minor one.
The other appendices recognized by the Terminologia Anatomica (and often not present): the fibrous appendix of the liver, the appendix of the testis (the hydatid of Morgani), and the appendix of the epididymis, the latter two being remnants of the and müllerian and mesonephric ducts respectively..
In only 30 percent of us does the vermiform appendix actually hang down from the cecum as is typically seen in diagrams and models; in the remaining 70% of the population it runs upward alongside the cecum and ascending colon. As is typical for structures without important functions, is quite variable in structure with lengths that usually vary from ¼ to over nine inches (with one record case of 13 inches). Check out the online Illustrated Encyclopedia of Human Anatomic Variation for additional details.
The earliest known drawing of the human appendix ("n"), done by Leonardo De Vinci around 1505. From O'Mally and Saunders 1952, Leonardo da Vinci on the human body