What is a piece of land surrounded by water called?

An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island in a river or a lake island may be called an eyot or ait, and a small island off the coast may be called a holm. Sedimentary islands in the Ganges delta are called chars. A grouping of geographically or geologically related islands, such as the Philippines, is referred to as an archipelago.

There are two main types of islands in the sea: continental and oceanic. There are also artificial islands, which are man-made.

Islets are very small islands.

There is no standard of size that distinguishes islands from continents, or from islets.

There is a difference between islands and continents in terms of geology. Continents are the largest landmass of a particular continental plate; this holds true for Australia, which sits on its own continental lithosphere and tectonic plate (the Australian Plate).

By contrast, islands are either extensions of the oceanic crust (e.g. volcanic islands), or belong to a continental plate containing a larger landmass (continental islands); the latter is the case of Greenland, which sits on the North American Plate.