An island (IPA: /ˈaɪlənd/) or isle (/ˈaɪl/) is any piece of land that is completely surrounded by water in two dimensions, above high tide, and isolated from other significant landmasses. Very small Islands such as emergent land features on atolls are called islets. A key or cay is another name for a small island or islet. An island in a river or lake may be called an eyot, /ˈaɪət/. There are two main types of Islands: continental Islands and oceanic Islands. There are also artificial Islands. A grouping of geographically and/or geologically related Islands is called an archipelago.There is no standard of size which distinguishes Islands from islets and continents.A special type of continental island is the microcontinental island, which results when a continent is rifted. Examples are Madagascar off Africa; the Kerguelen Islands; and some of the Seychelles.An atoll is an island formed from a coral reef that has grown on an eroded and submerged volcanic island. The reef rises to the surface of the water and forms a new island. Atolls are typically ring-shaped with a central lagoon. Examples include the Maldives in the Indian Ocean and Line Islands in the Pacific.