ETYM Greek; endo in + demos people: cf. French endémique.
1. (Ecology) Native to or confined to a certain region.
2. (Of disease or anything resembling a disease) Constantly present to greater or lesser extent in a particular locality.
3. Native; indigenous; generally present in a particular place or class.

A disease that is constantly present to a greater or lesser degree in people of a certain class or in people living in a particular location.
Of a disease, more or less prevalent in a given region or country all the time. It refers most often to tropical diseases, such as malaria, which are hard to eradicate.