I find it bizarre that the wargame answers are getting such a low response rate, since this is a multichoice pool. It seems obvious to me that, whatever the meaning is in relation to D&D, the term also means an old school wargamer, because that's where it comes from. Since there are people alive and kicking who were "grognards" back in the 70s, a redefinition that excludes them seems to me to be simply inaccurate if it aims to be useful.
Then again, maybe it's just become so hip to call old players "grognards" that many people are unaware of the wargame -> OD&D connection.