The difference between Great Britain, the United Kindom and the British Isles

Speaking of Britain, I know it's something I should know as a British citizen, but I can never keep it straight in my head, so let's see if writing it down helps: the difference between Great Britain, the United Kingdom and the British Isles.

Great Britain, often shortened to GB or just Britain, is a legal and political designation that includes England, Wales and Scotland. The United Kingdom (UK) includes England, Wales and Scotland, but also Northern Ireland (in fact, the official name of the sovereign nation, what it says on my passport, is "The United Kingdom of Great Britain and Northern Ireland"). The British Isles, on the other hand, is a purely geographical term with no legal or political standing, comprising England, Wales Scotland, the whole of Ireland, as well as the Channel Islands of Jersey and Guernsey and the Isle of Man (these latter islands being Crown Dependencies).

In practice, "Britain", "Great Britain" and "the UK" are used interchangeably, even in government documents, which is why things get confusing. In most cases, it doesn't really matter that much, unless of course you are taking to an Irish person (and, increasingly, a Scot or a Welsh person, many of whom don't want to anything to do with England, Britain or the United Kingdom).