They also had salt.apple.com and pepper.apple.com. And still functional: apple.apple.com

well I guess it doesn't stand for next step a, or they didn't need any more names than 'a' and never went for 'b' ;)

Also it could be "Next Step Administration", "Next Step Access", etc.. there are a billion possibilities, I'm not saying apple doesn't give access to NSA, they surely do, but I'm saying they obviously won't do it this way ;)