United Kingdom of Great Britain and Northern Ireland.

The Republic of Ireland is not in the United Kingdom or in Great Britain. Northern Ireland is in the United Kingdom, but not in Great Britain.

The Kingdom of Ireland and the Kingdom of Great Britain were united to form the United Kingdom of Great Britain and Ireland with the passing of the Acts of Union 1800. In this way, the United Kingdom became a single kingdom.

Great Britain is comprised of England, Scotland and Wales. When Northern Ireland is included, the country then gets its full title of 'The United Kingdom of Great Britain and Northern Ireland'.

The United Kingdom of Great Britain and Northern Ireland, often just called the United Kingdom or the UK.