Citation, DOI & article data
The epidemiological term endemic is used for any condition that persists within a particular community/locale without the need for external input of new disease, i.e. the disease in question has attained a steady-state in the affected population 1. For this to happen the basic reproductive number (R0) should be 1 or greater in theory, however in practice this tends to be an oversimplification, and diseases can continue under certain conditions with R0 <1.0 2.
History and etymology
Endemic is derived from the Classical Greek, ἐν (en) meaning "in" and δῆμος (demos) meaning "people".