Island
An island or isle 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 a lake island may be called an eyot or ait, and a small island off the coast may be called a holm. A grouping of geographically or geologically related islands is called an archipelago, such as the Philippines.
Britain (place name)
The term "Britain" is widely used as a common name for the sovereign state of the "United Kingdom", or UK for short. The United Kingdom includes three countries on the largest island, which can be called "the island of Britain" or "Great Britain": these are England, Scotland and Wales. However the United Kingdom also includes Northern Ireland on the neighbouring island of Ireland, the remainder of which is not part of the United Kingdom. "England" is not synonymous with "Britain", "Great Britain", or "United Kingdom".