What exactly defines production?

Like almost anyone who's been programming for a while, I'm familiar with the term "production code" and have a vague sense of what it means. However, can someone offer a semi-rigorous definition, since it seems Wikipedia and Google can't? It seems like there are a lot of gray areas in what counts as production, such as internal tools that are used by a small group of people and therefore not "formalized" in terms of UI, documentation, etc. and open source apps that are feature complete, reasonably bug free and working, but lack polish, UI and extensive testing.