From Wickipedia:
Hardcore gamer is a widely used term applied to describe a type of video game player. There is currently no unanimously agreed upon definition for the term. Some describe hardcore gamers as those whose leisure time is largely devoted to playing video games. This type of gamer prefers to take significant time and practice on games, in contrast to a casual gamer. Many hardcore gamers pride themselves on mastering the rules or use of a game, although this is not a strict requirement. Conflicting opinion argues that it is not so much the time spent on games however, as casual gamers can spend hundreds of hours on games without ever mastering them. Competition is another defining characteristic of hardcore gamers, who often compete in organized tournaments, leagues, or ranked play integrated into the game proper. In this light, professional gamers can be seen as an extreme example of hardcore gaming. It's also been said[by whom?] that "core" gamers or hardcore gamers is someone that plays a variety of games, master a large amount of games, and know a lot about the industry and history of video games
Video Gaming really never crossed my mind.
I immediately thought of LARPs and those folks that play. I think it depends on your experience what comes to mind. Then there's D&D and so on.