Explain common terms like "copyright", "patent" and "license"

Most people have a basic grasp of licensing-related stuff, but are hazy on the exact details of what the different terms mean. It would be nice if we could have a FAQ or something to explain all of it. I'd send a patch, but I'd like to solicit some feedback on what people think the exact format should be.

Here's a list of things we might want to put on such a page:
- "Copyright"
- "License"
- "Public Domain" (specifically the fact that waiving copyright law includes waiving your right to relicense, IIUC)
- "Patent" (especially since the distinction between a patent and a copyrighted work is lost on a lot of people)
- "Copyleft"
- Warranty disclaimers/liability (maybe?)