Stone in appendix
Literally, "lith" means stone.
An appendicolith is a finding (usually on cat scan or xray) reported by a radiologist when they see material that lights up in the appendix. Typically this is seen in the setting of appendicitis
but can also be an incidental finding. The stone is made up of hardened stool and is frequently the cause of appendicitis by blocking the opening and causing swelling.