An island /ˈaɪlənd/ or isle /ˈaɪl/ is any piece of sub-continental land that is surrounded by 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 an island in a lake may be called an eyot /ˈaɪ. ət/, or holm. A grouping of geographically or geologically related islands is called an archipelago.