I suppose a simple definition would be:

Casual: Someone who doesn't play as often, or is willing to play more family orientated games even if it's just on special occasions.
Core: Someone who plays regularly, supports thier console of choice but isn't obsessive about it.
Hardcore: Someone who plays games nonestop, buys everything they can and collects video games or consoles as a hobby.

There's more to it than that but that'll do.

What's the different between hardcore and core?

I would consider myself a core gamer. I use to be a hardcore gamer but with a wife, job, and other responsibilities, I just don't have the time I use to. Still trying to balance all of that out.

Edit: Got answered whle posting. Guess 'core' then. I do think that there should be some granularity where hardcore comes in, as I know some folks who play one specific game obsessively, and really nothing else.

I thought most VGC user are at least a core gamer because I think most people don't care about anything VGC provided.

To OP I considered myself as a core gamer since there are some games that I play competitively like Dota 2 and Smash. But I play most games just for fun.

Pretty hardcore. I average about 5 games a year bought, which would put me 3 to 4 times above the average attach rate.

I think the distinction is meaningless, but I waver between casual and core. I don't have the money to afford hardcore.

At the same time, there are people who spend thousands on mobile games, but some would still call them casual erroneously.

20 years of gaming, over 2000 games played, I would call myself hardcore.

I'm a core gamer since I don't play as much as I used to, even if I still buy games on a regular basis. I started playing videogames since I have memory (23 years more or less), and played on numerous consoles throughout the years. I sticked to Sony consoles for the past 17 years.

Every Nintendo gamer is a casual, while Xbox are hard core dude bro players and Playstation are the diversified crowd. Oh and pc "gamerz" play an hour a day on MOBAs and the rest on forums talking about amazing graphix games their pc only handle on medium (they are glorified casuals). I'm hardcorz. (Thank you for your teachings throughout the years Rol).