As it is apparent we can't decide on a definition on what is or even isn't OSR, at least beyond the same general definition of "pornography" - I know it when I see it, I've decided to go on a different track. (as an aside, the results of the previous post don't surprise me. Part of the strength of the OSR is it's diversity and the passion of the members of the gaming community that associate themselves as being part of the OSR. In this case, it isn't so much the path taken as it is the final destination)
Since the definition of the OSR is nebulous at best, and subjective in it's most simple terms, I've decided to take a different approach and ask the readers of The Tavern: "What is the OSR Ruleset of your choice or preference?" In other words, when you are looking to play some "old school gaming", what rulesets do you gravitate to?
There are no right or wrong answers, although I expect certain answers may lead to further questioning by other readers / commenters.
For me, the ruleset of choice would be Swords & Wizardry Complete, with bits borrowed from ACKS and the DCC RPG. I'd also so run AD&D1e, so long as the group in question were willing to play it as my groups played it in the 80s, not how it is actually written ;)