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.
Production means anything that you need to work reliably, and consistently.
Whether is a build script, or a public facing web server.
When others rely on your code, particularly folks who may not understand it (i.e. even "smart" developers but perhaps not in your group, but using a library you wrote), that code is production code.
It's production because "work stops" and "money is lost" when the production code fails.