Over a long period of history, the United Kingdom often changed the territory. This video explains some definitions about the places in the United Kingdom.
First, the United Kingdom is a country of countries: England, Scotland, Wales and Northern Ireland. The United Kingdom’s full name or original name is the United Kingdom of Great Britain and Northern Ireland. Great Britain is the largest island among the British Isles. Therefore, it is a geographical rather than a political term. The territory of United Kingdom contains Great Britain, Northern Ireland and the surrounding islands.
Secondly, the definitions about the British Empire: the Commonwealth Realm and the Crown Dependencies. The British Empire once spanned a 1/4th the worlds land and governed nearly a 1/4th its people. The former colonies that gained their independence through diplomacy and continue to recognize that authority of the crown are known as the Commonwealth Realm. They are, in decreasing order of population: Canada, Australia, Papua New Guinea, New Zealand, Jamaica, The Solomon Islands, Belize, The Bahamas, Barbados, Saint Lucia, Saint Vincent and the Grenadines, Grenada, Antigua and Barbuda, Saint Kitts and Nevis, and Tuvalu. All are independent nations but still recognize the monarchy as the head of state even though it has little real power within their borders. There are three further entities that belong to the crown and these are the Crown Dependencies: The Isle of Man, Jersey, Guernsey.
Thirdly, British Overseas Territories are the last vestiges of the British Empire. They have not become independent nations and continue to rely on the United Kingdom for military and economic assistance. The places are Bermuda, Cayman Islands,Turks and Caicos Islands, Gibraltar, The British Virgin Islands, Akrotiri and Dhekelia, Anguilla, Saint Helena, Ascension Islands, Tristan da Cunha, Montserrat, British Indian Ocean Territory, South Georgia and the South Sandwich Islands, Falkland Islands, British Antarctic Territory, Pitcairn Islands.