In our Mac 101 series, TUAW introduces basic OS X concepts to new Mac users. This is going to be a quick one, because there's not too much to it -- but it's a critical note when talking to other people in your newly adopted community.
Editor's Note: Please keep your comments civil and relevant. Remember that Mac 101 is aimed at novice users, not the grizzled Mac veterans who clearly are going to keep pronouncing things however the heck they want. Off-topic or abusive comments will be deleted; repeat offenders will be banned.
It's pronounced "Oh. Ess. Ten," not "Oh. Ess. Ex". (Yes, Apple has a KB article on this point.)
Mac OS X is a Unix-based operating system with roots reaching back to the Mach project at Carnegie Mellon and the NeXTStep OS in the late 1980's -- NeXT was a spin-off corporation founded by Steve Jobs during his exodus from Apple. Mac OS X was the version following Mac OS 9, even though the two systems are entirely different under the hood. The "X" is the Roman Numeral for ten.
It may look a little redundant when written out, but when you see "OS X 10.6.6", you can say "Oh. Ess. Ten. Point. Six. Point Six." or even "Oh. Ess. Ten. Six. Six." It's perfectly okay to drop the second ten.