So today I wanted to start learning Swift and Xcode 6.
I went to the Xcode download page, and I was like, hmm, what the hell is a GM seed?
As quoted from Wikipedia:
A copy of the RTM build known as the "gold master" or GM is sent for mass duplication
If you looked into the article, there's a pretty Software release life cycle map that shows you the different stages a software production goes through.
Usually I see software going from beta, and then to live or production. Gold master is something new.