RC = Release Candidate - Basically what we at the SCP think is almost a stable build. When we're ready to release we'll put up an RC build. If no major bugs are found in it, it will become an official build. RC's are therefore much more stable than normal nightly builds because we have spent a lot of time fixing bugs before we put up an RC build. But they're still less stable than an official release build.
Thank you for that, much clearer now. This is something else that will need to go into the 'dummies guide' :-)
Speaking of which, what does 'OP' mean here? That acronym has a lot of uses, some of them gaming related, such as 'Over Powered' and 'Observation Point'. This could be very confusing for newbies. I'm guessing in 'HLP-ese' OP stands for something different, but I cannot find an explanation as to what.