What is a AAA title?

It's come up a lot recently (for me at least) that Unity (supposedly) can't support AAA titles, and is mainly for prototyping when it comes to that stuff. That makes me wonder, what do people consider a AAA title, and what exactly makes them better?

AAA describes the $60 games that you buy in the shops. Big projects, big budgets. several hundred developers, mio of dollars in budget

Arguably, I would say Unity can do AAA quality games, its just that I haven't seen one yet. The closest I can point out is http://www.interstellarmarines.com/