At a glance, they may look the same but all three terms have fundamental differences among themselves.
The United Kingdom is used to describe the political unit consisting of England, Northern Ireland, Scotland and Wales.
Great Britain is the geographical term referring to the island simply known as Britain.
The United Kingdom of Great Britain and Northern Ireland (UK) is an island country that sits north-west of mainland Europe.
It is made up of mainland Great Britain (England, Wales and Scotland) and the northern part of the island of Ireland (Northern Ireland).
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the north-western coast of the continental mainland.
It comprises England, Scotland, Wales, and Northern Ireland.