A species is said to be endemic when its distribution is restricted to a specific area.
This area must be specified – the word endemic used on its own is meaningless, unless it is clear from the context!
Ultimately, all species are endemic to planet Earth! The term becomes most useful when the species is restricted to a relatively small area, such as a country or a biome. For example, the Cape Bulbul is endemic to South Africa, and the Cape Sugarbird is endemic to the Fynbos Biome.
The use of the term endemic is not restricted to species. It can be used for subspecies, or for a genus, family, etc. For example, the order Coliiformes is endemic to Africa – this means that the six species of mousebirds only occur on the continent of Africa. The only other bird order endemic to Africa is the Musophagiformes, which contains all the Turacos.