The islands of Great Britain and Ireland are part of an archipelago with a combined area of 315,000 km² off the west coast of Europe, and the term "Britain and Ireland" is sometimes used, somewhat loosely and incorrectly, to refer to that entire archipelago. This archipelago is often called the "British Isles"; some people believe one should avoid using this term because it could be construed as having the incorrect or politically loaded implication that the Republic of Ireland is or should be part of the United Kingdom.

More commonly, the term "Britain and Ireland" is used to refer to the two states within the archipelago, namely the United Kingdom of Great Britain and Northern Ireland (comprising England, Scotland, Wales and Northern Ireland) and the Republic of Ireland. Depending on the context, it may or may not include the smaller islands that are part of these two states and lie around the coasts of the two major islands; used correctly, it does not include the Isle of Man or the Channel Islands even though the Isle of Man forms part of the British Isles and the Channel Islands are often taken as also doing so.

In the context of the Northern Ireland peace process the term "Islands of the North Atlantic" (IONA) has been used as a neutral term to describe these islands, though that term has also be labeled ambiguous.