A deserted island or uninhabited island is an island that is not permanently populated by humans. Uninhabited islands are often used in movies or stories about shipwrecked people, and are also used as stereotypes for the idea of "paradise". Some uninhabited islands are protected as nature reserves and some are privately owned. Devon Island in Canada is claimed to be the largest uninhabited island in the world.
Small coral atolls or islands usually have no source of fresh water, but at times a fresh water lens (Ghyben–Herzberg lens) can be reached with a well.
Uninhabited islands are sometimes also called "deserted islands" or "desert islands". In the latter, the adjective "desert" connotes not desert climate conditions, but rather "desolate and sparsely occupied or unoccupied". The word "desert" has been "formerly applied more widely to any wild, uninhabited region, including forest-land", and it is this archaic meaning that appears in the phrase "desert island". Similarly, the term "deserted island" does not imply that the island was previously inhabited and later deserted.
The term "desert island" is also commonly used figuratively to refer to objects or behavior in conditions of social isolation and limited material means. Behavior on a desert island is a common thought experiment, for example, "desert island morality".
The first known novels to be set on a desert island were Philosophus Autodidactus written by Ibn Tufail (1105–1185), followed by Theologus Autodidactus written by Ibn al-Nafis (1213–1288). The protagonists in both (Hayy in Philosophus Autodidactus and Kamil in Theologus Autodidactus) are feral children living in seclusion on a deserted island, until they eventually come in contact with castaways from the outside world who are stranded on the island. The story of Theologus Autodidactus, however, extends beyond the deserted island setting when the castaways take Kamil back to civilization with them.