Hardcore... How would you define it?

[Dorin]

I distinguish Hard-Core and Casual via attitude.

A Hard-Core player is serious and treats the game like a high-stakes gambling or sporting event in which they are the player. They care very much about the success of their endeavors, and want their game-mates to have the same attitude. They might spend hours researching raids or the best equipment sets, or figuring our exactly what combination of skills, gear, and ancillary items will make them the best they can be.

A Casual player is someone who does not value success as highly, and plays the game for "light hearted" enjoyment. They may spend a lot of time in the game, and it may be spent on the same content, but their attitude might be one of, "Hey if we get it, cool, if we don't - I had some fun!" They probably are not going to spend long hours to accomplish the same goals or minute advantages a "Hard-Core" player might.

I don't think one is better than the other, I tend to get into sporadic bursts of one or the other.

Pretty good and accurate descriptions actually, I agree with you.