United Kingdom, island country located off the northwestern coast of mainland Europe. It comprises the whole of the island of Great Britain—which contains England, Wales, and Scotland—as well as the northern portion of the island of Ireland. Its capital is London.
The United Kingdom of Great Britain and Northern Ireland is a unitary state with a constitutional monarchy. Scotland, Wales and Northern Ireland have a degree of autonomous devolved power.
While many people use the terms United Kingdom, Great Britain, and England interchangeably, there is a difference between them—one is a country, the second is an island, and the third is a part of an island.
Great Britain, therefore, is a geographic term referring to the island also known simply as Britain. It’s also a political term for the part of the United Kingdom made up of England, Scotland, and Wales (including the outlying islands that they administer, such as the Isle of Wight).