Initialism

UK

1. United Kingdom of Great Britain.
2. United Kingdom of Great Britain and Ireland.
3. United Kingdom of Great Britain and Northern Ireland.

The United Kingdom of Great Britain and Northern Ireland (commonly known as the United Kingdom, the UK, sometimes Britain) is a sovereign state located off the northwestern coast of continental Europe. It is an island country, spanning an archipelago including Great Britain, the northeastern part of the island of Ireland, and many small islands. Northern Ireland is the only part of the UK with a land border, sharing it with the Republic of Ireland. Apart from this land border, the UK is surrounded by the Atlantic Ocean, the North Sea, the English Channel and the Irish Sea. Great Britain is linked to France by the Channel Tunnel.

The United Kingdom is a constitutional monarchy and unitary state consisting of four countries: England, Northern Ireland, Scotland and Wales. It is governed by a parliamentary system with its seat of government in London, the capital, but with three devolved national administrations of varying powers in Belfast, Cardiff and Edinburgh, the capitals of Northern Ireland, Wales and Scotland respectively. The Channel Island bailiwicks of Jersey and Guernsey, and the Isle of Man are Crown Dependencies, which means they are constitutionally tied to the British monarch but are not part of the UK. The UK has fourteen overseas territories that are not constitutionally part of the UK. These territories are remnants of the British Empire, which at its height in 1922 encompassed almost a quarter of the world's land surface, the largest empire in history. British influence can still be observed in the language, culture and legal systems of many of its former colonies.

The UK is a developed country, with the world's sixth largest economy by nominal GDP and the sixth largest by purchasing power parity. It was the world's first industrialised country and the world's foremost power during the 19th and early 20th centuries, but the economic and social cost of two world wars and the decline of its empire in the latter half of the 20th century diminished its leading role in global affairs. The UK nevertheless remains a great power with strong economic, cultural, military, scientific and political influence. It is a recognised nuclear weapons state while its military expenditure ranks third or fourth in the world. (Depending on calculation according to SIPRI) It is a Member State of the European Union, a permanent member of the United Nations Security Council, a member of the Commonwealth of Nations, G8, G20, NATO, OECD and the World Trade Organization.