I was very happy to stumble upon (thanks Ed) this explanation of the terms United Kingdom, Great Britain, etc.—via a Venn diagram. The precise definitions of these terms have always confused me. It was created by Sam Hughes.

Follow the link to his page to read a more detailed discussion of the terms. My favorite line was the last one in which he wrote:

Lastly, to be pedantic, this is actually an Euler diagram, not a Venn diagram.