Casual gamers are the people who mostly own console systems and buy mostly sports and racing games. They don't like fantasy games and only enjoy sci-fi games based on movies they may have seen. This group, unfortunatly, makes up the bulk of the gaming community and the current popularity of shitty games on shitty console systems is evidence of this. Casual Gamers think that having a "life" consists entirely of getting laid and drunk on a regular basis and have very little interest in games outside of a way to pass the time without spending alot of money.
The group of people who call themselves Hardcore gamers aren't often quite as "hardcore" about gaming as they would like to think. These are the people you see complaining that games now come in fancy modes like "3D" and debating the finer points of why Final Fantasy 6 was better than Final Fantasy 7. The only people who might actually be hardcore are the people who sit an camp the firegiant hideout in evercamp for 72 hours at a time just to get some item that will help them camp better. I wouldn't rate either side of this coin as being a very pretty sight.
Finally there are the true gamers who actually treat gaming as a real HOBBY and not just a way to pass time or something to try and collect hundred upon thousands of. True Gamers just try to find an enjoy the best games out there and don't like getting ripped off because Casual gamers are pushing the industry towards a point where the only games that will be profitable are Madden and GTA. True Gamers often own high quality PC's and play PC games most often. Despite what most people might think a PC isn't hard to operate and doesn't cost too much. The people who say PC's are too expensive are often spending hundreds of dollars on console systems that can't do even half as many things as a PC can do and to make matters worse they own more than one of these stone age devices.
Any other stereotypical definition is useless: I play online games a lot. I am over 40, have a girlfriend, am in good physical shape and I hold down a fairly high-pressure job. I am college educated.
Some of the younger gamers that I meet online fit the nerdy stereotype but no more than the average cross-section of high-school students. There is a higher than average number of creative professionals in the game servers I go to (probably because I go to the Mac servers).
I also have LAN parties at my house - my friends come round, we drink a few beers, get a take-away, link our computers together and fight to the death. The other three are married and two have kids. Three of us have college degrees and we are all fairly high earners.
Your stereotype is way off.
Though the percentage of people who participate in such activities has increased in recent years, a certain stigma still surrounds those elite few who can call themselves "true gamers". These are the people you see getting together for a rousing session of Dungeons & Dragons once a week, or who you will regularly see planted in front of a TV or computer monitor, immersed in the bliss of gamedom.
This is not to say gamers are the bespectacled hermits that the stereotype has long been. We are everywhere, in many shapes and forms. We live and breathe the likes of Halo, Warcraft, Unreal Tournament, Mage: The Ascension, and more. And the gamer is here to stay.
Participants in the tabletop roleplaying game Dungeons & Dragons inherently deserve the title of "gamer".