The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a sovereign country in western Europe. Lying off the north-western coast of the European mainland, the UK includes the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands. Northern Ireland is the only part of the United Kingdom that shares a land border with another sovereign state—the Republic of Ireland.[note 9] Apart from this land border, the UK is surrounded by the Atlantic Ocean, with the North Sea to its east, the English Channel to its south and the Celtic Sea to its south-south-west, giving it the 12th-longest coastline in the world. The Irish Sea lies between Great Britain and Ireland. With an area of 242,500 square kilometres (93,600 sq mi), the UK is the 78th-largest sovereign state in the world. It is also the 21st-most populous country, with an estimated 65.5 million inhabitants in 2016.
Prior to the creation of the UK, Wales had been conquered and annexed by the Kingdom of England. This meant that the United Kingdom created in 1707 by the Treaty of Union between England and Scotland encompassed all of Great Britain. The Kingdom of Ireland merged with this state in 1801 to form the United Kingdom of Great Britain and Ireland. Five-sixths of Ireland seceded from the UK in 1922, leaving the present formulation of the United Kingdom of Great Britain and Northern Ireland. There are fourteen British Overseas Territories,[20] the remnants of the British Empire which, at its height in the 1920s, encompassed almost a quarter of the world's land mass and was the largest empire in history. British influence can be observed in the language, culture and legal systems of many of its former colonies.
The UK is a developed country and has the world's fifth-largest economy by nominal GDP and ninth-largest economy by purchasing power parity. It has a high-income economy and has a "very high" Human Development Index, ranking 16th in the world. It was the first industrialised country and the world's foremost power during the 19th and early 20th centuries. The UK remains a great powerwith considerable economic, cultural, military, scientific and political influence internationally. It is a recognised nuclear weapons state and is sixth in military expenditure in the world.[25] It has been a permanent member of the United Nations Security Council since its first session in 1946. It has been a leading member state of the European Union (EU) and its predecessor, the European Economic Community (EEC), since 1973; however, a referendum in 2016 resulted in 51.9% of UK voters favouring leaving the EU, and the country's exit is being negotiated. The UK is also a member of the Commonwealth of Nations, the Council of Europe, the G7, the G20, NATO, the Organisation for Economic Co-operation and Development (OECD), Interpol and the World Trade Organization (WTO).
The 1707 Acts of Union declared that the kingdoms of England and Scotland were "United into One Kingdom by the Name of Great Britain", though the new state is also referred to in the Acts as the "Kingdom of Great Britain", "United Kingdom of Great Britain" and "United Kingdom".The term "United Kingdom" is found in informal use during the 18th century and the country was also occasionally referred to as the "United Kingdom of Great Britain" though its full official name, from 1707 to 1800, was merely "Great Britain", without a "long form". The Acts of Union 1800 united the Kingdom of Great Britain and the Kingdom of Ireland in 1801, forming the United Kingdom of Great Britain and Ireland. Following the partition of Ireland and the independence of the Irish Free State in 1922, which left Northern Ireland as the only part of the island of Ireland within the United Kingdom, the name "United Kingdom of Great Britain and Northern Ireland" was adopted.
Although the United Kingdom, as a sovereign state, is a country, England, Scotland, Wales and, to a lesser degree, Northern Ireland are also regarded as countries, though they are not sovereign states. Scotland, Wales and Northern Ireland have devolved self-government. The British Prime Minister's website has used the phrase "countries within a country" to describe the United Kingdom. Some statistical summaries, such as those for the twelve NUTS 1 regions of the United Kingdom, also refer to Scotland, Wales and Northern Ireland as "regions". Northern Ireland is also referred to as a "province".With regard to Northern Ireland, the descriptive name used "can be controversial, with the choice often revealing one's political preferences".
The term "Britain" is often used as a synonym for the United Kingdom. The term "Great Britain", by contrast, refers conventionally to the island of Great Britain, or politically to England, Scotland and Wales in combination. However, it is sometimes used as a loose synonym for the United Kingdom as a whole. GB and GBR are the standard country codes for the United Kingdom (see ISO 3166-2 and ISO 3166-1 alpha-3) and are consequently used by international organisations to refer to the United Kingdom. Additionally, the United Kingdom's Olympic team competes under the name "Great Britain" or "Team GB".
The adjective "British" is commonly used to refer to matters relating to the United Kingdom. The term has no definite legal connotation, but is used in law to refer to United Kingdom citizenship and matters to do with nationality.[50] People of the United Kingdom use a number of different terms to describe their national identity and may identify themselves as being British; or as being English, Scottish, Welsh, Northern Irish, or Irish; or as being both.
In Welsh, the long form name of the state is "Teyrnas Unedig Prydain Fawr a Gogledd Iwerddon", with "Teyrnas Unedig" being used as a short form name on government websites.[53] However, it is usually abbreviated to "DU" for the mutated form "Y Deyrnas Unedig". In Scottish Gaelic, the long form is "Rìoghachd Aonaichte Bhreatainn is Èireann a Tuath" and the short form "Rìoghachd Aonaichte".