I know these topics come up from time to time, but I'm a little curious on how people usually use these word. I don't try to use these words, but it happens by mistake. I'm gonna try to give several definition with examples.
1) how much you play on average per day. example: You're a hardcore gamer if you play on average 5 hours per day.
With this Definition I would have to say I'm a Casual Gamer, cause on a typical weekday I play about 2 hours and on weekends I try to play as much as I can, but I usually get sick after 4hours of gameplay and I have to turn the game off.
2) how many times you play a game. This definition depends on what game is hardcore for you. example: if you play a game at least 3 times you're a hardcore player.
With this Definition, it depends. I'm a Hardcore player when I play Biohazard 4 since I've played that game 8 times, but I'm a Casual player with most RPGs like FF10 or DQ8, since I've only played each of those 1 time
3) how long the game actually is without wasting time. This definition depends on what game is hardcore for you. example: RPGs take 40 hours to finish so therefore it's a hardcore game.
With this Definition, like above it depends. It's the reverse of the above for me. I'm a Hardcore player with most RPGs like FF10 or DQ8 since they take at least 40 hours to finish, but I'm a casual player for Biohazard 4 since it takes like 7 hours to finish the game.
This definition can take another example. IF you DO waste time then you're a casual gamer. Like my cousin he has played every GTA game since 3, and I haven't seen him do 1 mission, NOT 1. All he does is just kills people. Personally a person wanting to finish the game is a more hardcore gamer than a person that just wants to randonly kill people. Right now I'm not sure if this part should go on the above definition.
4) what difficulty you play the game on. You're a hardcore player because you play on the hardest difficulty. This definition depends on what game is hardcore for you.
With this Definition, like above it depends. For me I'm a Casual player for most games since I usually play on the Normal Difficulty, but I"m a Hardcore gamer for Biohazard 4 since I beat the game in the highest difficulty.
5) SD vs. HD. You're a hardcore gamer if you play games on a HD console.
With this definition, I'm a contradiction. I own a Wii which makes me a casual gamer, but I also own a 360 which makes me a hardcore gamer.......that's a contradiction, but I guess some people use it.
6) rating. example: You're a hardcore player if you play a game that has at least a Teen rating.
With this Definition, I'm a hardcore player since I play Biohazard 4 (rated Mature) but a casual player cause I play new super mario bro Wii-hii :D (rated Everyone).
7) perfection. You're a hardcore gamer if you get EVERYTHING in a game. This definition depends on what game is hardcore for you.
With this Definition, I'm almost always a casual player. Getting all Heart tanks in Zelda games, and probably getting all of Lost Odyssey and maybe Blue Dragon's achievments, I'm hardcore at those. You can argue that I'm not a Lost Odyssey Hardcore gamer cause I might have gotten all the achievements, but I didn't get to max level with everyone.
I can't think of any other definition, let me know and I'll add them if they apply. Personally I think when people use any of these 2 words, I think they're idiots (sorry for insulting) who are trying to make themselves feel better. This is the reason why no one knows what you're talking about when you use any of those 2 words, cause they have different meaning to different people. Mine would be probably 1, 2 or 7, but like I said I don't try to use those words.