I like this definition. It's a very nuanced analysis of the dynamic between the two groups.

And if we go by d21lewis' definition, and again I think it's a good one, then the casual gamers outnumber the hardcore gamers by a substantial margin.

Which is just one more reason to be as inclusive as possible. It doesn't make much sense to alienate the majority of people playing video games. I mean, if we all love video games, wouldn't we want to share them with as many people of possible? I for one take a lot of pride in sharing video games with people who know less about them.

In response to Richard...

A lot of great points. You're definitely right that the industry is experiencing growing pains. Video games have never before been so big and so mainstream.

I think a lot of animosity between "hardcore" and "casual" gamer stems from the fact that for about 30 years video games weren't taken very seriously as a medium or as an art form outside of a dedicated group of people who played them. Today video games are much more popular and mainstream than ever before. So I think a lot of people who grew up with video games feel uncomfortable with its popularity.

I would say that one of the primary differences between the two groups is how the medium is conceptualized. Core gamers tend to view video games as something greater than just a simple time waster ... whether it be a passion (that they may have a desire to turn into a career), a competitive sport (whether they participate in leagues or not), or a whole new artform (the interactive storytelling crowd).

I think it comes down to commitment. Maybe this analogy makes it simpler...

a casual gamer is to a core gamer as a kid who doodles in his notebook during class is to a professional painter

There is a casual/core crowd split in pretty much any activity, art, or field of study. As another example, I go bowling at a local lane every couple of weeks to a month or so depending on time constraints. Clearly this puts me into the "casual" crowd as I know guys that are there almost every day practicing and participating in leagues whenever they can. We are both "bowlers" but there is a clear difference in interest level and commitment. It is a passion for them, and a fun diversion for me. 

Frankly I find 'hardcore' gamers whine about difficulty a lot more than casual gamers do because casual gamers aren't playing games that are generally that hard to being with*, unless we start breaking out hardcore into tiers starting with the bitch kitty COD players at the top and the Dark Souls players at the bottom (or vice-versa). 

The point is, the hardcore you're talking about, that actually care about this hardcore-casual dvidie/dichtomy, are a microscopic part of the market so, really,  who gives a **** what they think?

Christ, I'm as hardcore as gamers come, yet I have more animosity towards core gamers than casuals precisly because this microscopic minority of gamers feels entitled to judge who and who isn't a 'core' gamer over something as utterly trivial and banal as video games.

(And in my experience, the so-called casual gamers have no idea that this dichotomy even exists because they're too busy playing and enjoying what they like than to spend time navel-gazing about a conflict that only really exists in the minds of a bunch of shut-ins that are pissed that "oh no, someone other than me and my shut-in friends are enjoying games but not the games I enjoy, so those casual bastards suck and are destroying the hobby that I just picked up in the last 6-8 years so I'm totally in a position to judge who and who isn't a real gamer. Cause I"m a shut-in. With no life. Who lives for imaginary conflicts because real-life conflicts dont'exist for me. Because I'm a shut-in loser." Yeah.)

*Point of order: the latest Mario is much, much harder than the latest COD.

There is likely some hipsterism involved here:

http://en.wikipedia.org/wiki/Hipster_(contemporary_subculture)

You have something go mainstream and the core feel like their superior indie stuff is now respectable and feel they are threatened by things.

Core gamers-
-Highly invested in games
-like the challenge of games
-Will learn movesets and intricate details of a game and figure out how to apply it to their advantage in games
-Know ahead of time when key games are coming out.
-Invest their time in talking about games and going on sites (like this one).
-Have taste in games because they've played so many. They know what they like and don't like.
-Have taste in technology and consoles, even though they might like have all of the ones that are out.
-Gaming has a social and cultural affect on them.
-Can play everything from easy to extremely hard games.

Casuals

-Not invested in gaming.
-Do not know about what games are coming out, except for a few key first party games that are either bundled or heavily commercialized.
-Do not care about the intricacies of gaming. They just want to have fun.
-They like social games (core gamers do too, but these guys are the bulk of the sales).
-They don't care to go on forums to talk about games. There are other hobbies they will talk about though.
-Gaming has no social or cultural effect on them.
- Doesn't generally want to be challenged. T
-likes new experiences (same with core, but these guys are the bulk of the sales).
-Simple controls/pick up and play.

Somebody summed it up in a single word. I won't give them the honor of being called by name, though. That word:

Passion.