Endo, Intra, and ENTO are all prefixes that mean 'WITHIN'. Endo is derived from the Greek word 'endon' meaning 'WITHIN', Intra is derived from the Latin word 'intus' meaning 'WITHIN', and ENTO is derived from the Greek word 'entos' meaning 'WITHIN'. These prefixes are used to describe something that is located WITHIN a certain area or boundary. For example, endoscopic surgery is a type of surgery that is performed WITHIN the body using a specialized instrument. Intravenous therapy is a type of medical treatment that involves administering medication directly into the bloodstream. Entomology is the study of insects and other arthropods that live WITHIN a certain environment.