The name "Golden Master" evokes a level of martial arts proficiency or maybe even a final cut of a film. I think context clues provide adequate explanation of a Golden Master release. I would define it as the version of a software [product] that has been approved as the release version following a pre-determined phase of development completion and testing.
If my definition is nearly accurate, what is the genesis of the term Golden Master? Apple is famous for their iOs, OSX GM candidate releases and I have yet to hear anyone else use the same term.