An alternative name for Great Britain. Sometimes also used to refer to the whole of the United Kingdom, although this can be a bit confusing.

a monarchy in northwestern Europe occupying most of the British Isles; divided into England and Scotland and Wales and Northern Ireland

an integral part of Europe (whether she likes it or not)

The group of countries comprised of England, Wales, Scotland and part of Ireland. In the past Britain created a great empire that explored and claimed land around the world as colonies. Some of the British colonies eventually became the provinces of Canada.

The word Britain is an informal term used (for brevity or convenience) when referring to;

London