Further reading

http://en.wikipedia.org/wiki/Software_release_life_cycle#Release_to_manufacturing_.28RTM.29

And the term dates back to:

http://en.wikipedia.org/wiki/Master_recording

A funny bit of trivia -- when Valve shipped Half-Life 1, they had all their code in a directory named "src" (source code). When it went gold, they renamed that directory to "GoldSrc", and made a second copy called "Source".

They kept maintaining the "GoldSrc" code-base with patches / expansions for Half-Life 1, while all their new features were made to the "Source" version that became Half-Life 2.

They never actually came up with a name for their engines, so they called the HL1 engine "the GoldSrc engine", and the HL2 engine "the Source engine". Lazy bastards!

Thanks for the articles. Nice reads.

That is a funny trivia. Smart people. They planned ahead and made money off of an existing codebase.