No, it's not just semantics. Betas are pre-release versions, which means that some functionality may not be present.
That's actually not how the term "beta" has been traditionally used.
"Alpha" releases are development versions, where features may not be finished yet or even ones that are planned are not yet present at all.
"Beta" occurs
after a feature freeze, and is strictly supposed to be a release that people are testing for correctness of functionality (
i.e., bugs). No new features should be getting added during "beta" and expected/planned functionality should be 100% present even if rough around the edges.
"Release Candidate" is, hey, barring the discovery of some showstopper bug, we aren't changing a thing, and this release is a
candidate for potentially being what we ship to customers. ("Golden Master Candidate" is, I believe, Apple's name for "Release Candidate." If people would abbreviate these last few Yosemite releases as,
e.g., GMC3 instead of GM3, that might help go a ways to quelling these kinds of naming disputes.)
"Golden Master" (sans the "Candidate" part) is what gets sent to the mastering plant for duplication and shipment. Typically, once GM gets sent to manufacturing, it's too late to recall it.
Of course, these days we are living in a world where because software is distributable over the network, software testing and releases and release schedules can end up being a little bit more...fluid than they have been in the past. This has both positive and negative aspects to it. There are a definitely a few software companies that I have had run-ins with who call what should be "alpha" releases "beta", and what should be called "beta" they call "release candidates."
I don't know what happened before Public Beta 1 with the Developer Previews (since I ain't a developer), but it certainly seems to me that through the course of the Yosemite development and testing process (at least the parts that the public was exposed to), Apple has generally stuck pretty consistently with the traditional uses of these terms. Certainly by PB1 I would say Yosemite was pretty darn close to feature complete...maybe 95% complete at the worst. And the GMCs I think are releases that Apple honestly could have seen themselves actually shipping to customers. Consider how small the change-sets have been between GMCs 1, 2, and 3. We are talking 50MB updates compared to 700MB-1GB updates we were seeing between PBs. That tells you something right there.
-- Nathan