MovieBob came up with a pretty good definition of a hardcore gamer during one of his Game Overthinker videos a long time ago. Apologies in advance if I don't quote it exactly right:
"Hardcore gamers are video game players who hold video games as one of, if not THE, central forms of entertainment of their spare time. Casual gamers, by contrast, are people who see video games as just a means of killing time every now and again."
"Hardcore gamers are video game players who hold video games as one of, if not THE, central forms of entertainment of their spare time. Casual gamers, by contrast, are people who see video games as just a means of killing time every now and again."