As far as I'm concerned, what "type" of "gamer" you are has got nothing to do with what you've played, how much you play, how long you've been playing games for or how good you are at them.
It is 100% in my honest opinion, a PASSION FOR GAMING that makes you a GAMER.
If you have a PS3, and an Xbox360 a Wii and a top end PC, but you don't really play them much, or would rather do other things and just hit up the odd bit of MW2, Wii Sports or Mario now and then - you are not a gamer in my book.
If you have only got a Wii, but you LOVE it, spend your time reading about forthcoming games and hunting out rareties, counting the days till the next big release - YOU ARE A GAMER.
My friend has a Wii and a PS3, I've spent the last week trying to persuade him to get Red Dead Redemption, he has always been a massive fan of Grand Theft Auto games and I'm trying to tell him that Red Dead is right up his street, he's not really bothered, he'll probably pick it up when it's less than half price and no-one else is playing it anymore. The one and only game he's bought in the last year, was MW2 (he has PLENTY of expendable money) and he plays that now and then, I lent him Fallout 3 many months ago, he hasn't touched it. I consider him a casual gamer.
My other buddy, is 46 has 2 kids and a seriously hot wife (unrelated to the story). He's got a Wii and a PS3 too. (not to mention a house littered with PSP's, DS's and DSI's.
He is shite at playing games! Fucking terrible. Watching him play RDR was nothing more than painful, despite having played GTA4 he just didn't understand the concept of cover, or how the auto aiming worked. Watching him crouching wiggling his corsshair around trying to get it somewhere near his target was literally hurting my eyes. He CANNOT handle online PvP games ("wah wah I can't kill anyone, wah wah got killed AGAIN") and he mostly plays Tower Defence games, Savage Moon being his game of choice, he has one more trophy to get on that.
But he's always got his eye on forthcoming games, he ALWAYS buys the AAA games at launch, more often than not buys the guide books too (I'm not a fan of playing games "by-the-book" myself), comes to midnight launches with me and is often asking "Have you heard about this game?" He loves his gaming t-shrits and proudly wears them everywhere.
He is a gamer in my book, perhaps even a hardcore gamer.
My Dad was wandering past a game shop when the Wii first launched (while there were serious stock shortages) dropped in and asked "Do you have one of those Wii things?" strangely enough they had just received a shipment and had 2 spare! He bought one, with WiiSports, Need for Speed and Tiger Woods. I later bought the godfather for his wii and mum saw WiiFit on TV so he got that for her. Later I bought him Rapalla fishing frenzy for his birthday.
He played a little rapalla with me on his birthday and forgot it existed. Mum got bored of Wiifit in a week and now my sister has bought Guitar Hero for it and when she comes back from uni plays that, occasionaly. Now and then my little cousins come over and will crack out the WiiSorts, but that's about it.
My family are not gamers, they're not even casual gamers.
I ONLY have a PS3 and a PSP, a piss poor laptop that won't play games and that's it.
I play games every day without fail, in my lunchbreak i go home and play an hour of whatever has my interest at the time. I read Dtoid every single day, very rarely miss a front page post, I know when games are due to come out and i have an account at the local store full of pre-orders. I get excited on Wednesdays (used to be Thursdays) to check out what's new on the PSN store, it's the first thing i do after work.
I thrive on Multiplayer but also love a good story, I play AAA games, weird rare games, downloadables, Japanese games ANYTHING. I often play games when I should be doing other things, I often spend money that should be spent on other things on games. My gaming habit sometimes gets me in trouble. I always stay up late playing games and it makes me tired at work.
I'm a hardcore gamer, I'd even happily say that I'm an addict.
So yeah, that's how I define the thre types of gamer.
Casual Gamer - Doesn't really care about games, couldn't tell you what the next AAA game is.
Gamer - Cares enough to know when the next big game is coming out, will buy it, but will only play it when they have some time to kill.
Hardcore gamer - Has that shit pre-ordered and is counting down the days, will sacrifice other things to get it and to play it on launch day, will probably play it for long extended periods, often until they fall asleep, controller in hand.