These are Standard names for that island realm or for parts of it. Technically, Great Britain (plus some of the small offshore islands such as Wight and Skye) is the main island, containing England. Scotland, and Wales, although jurisdictionally the term is also used for the main island plus Northern Ireland. Britain is simply a convenient and familiar Informal clipped form of Great Britain. The “United Kingdom of Great Britain and Northern Ireland” is the full official title of this European country, often shortened to (the) United Kingdom, or to (the) U.K., pronounced as the names of the two letters. (The) British Isles is the term used for the geographical area itself, including the main island, Ireland (containing Northern Ireland and the independent country Eire), and numerous small offshore islands.