Yea, there's lots of good info on XDA coming from good people, but too many of them think they're the love-child of Mr.Miyagi and Yoda. lol
Here -in a nutshell- is how release versions are generally coded:
Alpha: for developer testing only; many inherent bugs that require other people who understand coding and such to assist with working on. Not ready for mass consumption, period. There can be different stages of useability here, but suffice it to say, that unless you know how to work under the hood (so to speak), don't touch an Alpha release.
Beta: Still in testing stage, but generally fit for public consumption as most major immediate flaws have been ironed out and just some system bugs remain with UI tweeks to be made as well. Like with Alpha, there are different stages of beta release as well, but they are all varying degrees of "generally useable but not entirely ready to be a daily driver".
RC: This stands for Release Candidate. Imagine a mother bird choosing which of her chicks to kick out of the nest first. The RC is the one she's chosen, so while it's still not fully baked in the sense that it isn't a completely air-tight product from both system and UI perspectives, it's definitely capable of being a daily driver for the avg person, as well as for the person with moderately sophisticated needs. Varying degrees of this step as well (RC2, RC3, etc), but typically when you're looking at a release candidate version of software/firmware, it's close enough to "fully baked" to where you can rely on it to work for you with consistency.
Please know that I am by no means one of the pseudo-Yoda's I reference above and have really learned most of the above info over the last few years of playing with these devices and bouncing ideas off others who know better than me. Saying all this to say that there are certainly others here and elsewhere who can elaborate on this, but for layman's purposes, this should do the trick.
-Ryan