From the Greek ἔνδημος "local."

Endemism - the distribution of organisms in a particular geographic area.

Endemic species are characterised by a very small, restricted range. Apart from them, endemics are found nowhere else.

Oceanic islands and waters isolated from other waters with similar biotic characteristics are the richest in endemic forms. For example, the flora and fauna of Lake Baikal contain up to 75% of endemic species.