A hardcore gamer, or whatever you would like to call it, would at least require a dedicated gaming machine of some sort. They would also regularly dedicate some of their free time for the purpose of gaming, because they enjoy it so much.
I think that pretty much sums it up.

This is the first reply I take issue with, this would mean only the well off PC players can be hardcore. 

theoretically I guess it would be based on experience in gaming
Casual gamer - Below Average
Gamer - Average
Hardcore Gamer - Above Average
Not that I've ever used the term but it's what I think when other do

Do you have to be above average in many genres or does one just count, cause I'm well above average at souls and non combo action games like Sekiro or Stellarblade but on FPS games my skills have slipped from that mark in the last 15 years to probably casual. 

Good for you. I can consistently beat Mike Tyson's Punch-Out!! in about 18-17 minutes. But no one cares about those things xD

I was jesting but I do care actually, that's really impressive. Be proud of it. I find pride in my ability to beat Sekiro in under 4 hours. Feels good even if I'm only praising myself. 

To be a hardcore gamer you have to get the high score on Defender at the local arcade.

No life incel that only sits inside and plays games.

Should go out now and then to play in the snow or get some sunlight and interact with people.

Well, for me it has nothing to do with skill. Just someone that explores different genres, dedicates time, is generally knowledgeable about the gaming industry.