Grognard is a slang term for someone who enjoys playing wargames (and strategy games in general). Originally it referred to table-top gamers, but now, by extension, it's also used for computer gamers.

In the old Jeff Foxworthy "redneck" tradition: If you enjoy reading 300 page manuals for your games, you may be a grognard. If you sometimes find yourself staring at a strategy game map at 4 AM, and you keep mumbling "just one more turn", you're probably a grognard. If the game represents planes by plus signs and ships by 0's, you're definitely a grognard.

The word was originally used to describe veteran soldiers in Napoleon's army - in French, it can be translated as "grumbler".