Definition from Wiktionary, the free dictionary
Alternative forms 
- Having an extreme dedication to a certain activity; diehard.
- He's a hardcore gamer.
- (slang) Particularly intense; thrillingly dangerous or erratic; desirably violent in appearance; pleasing or "cool" due to intensity or danger.
- That show was hardcore, dude.
- Resistant to change.
- Obscene or explicit.
- (pornography) Of or pertaining to pornography that depicts penetration.
- (music) Faster or more intense than the regular style.
having an extreme dedication to a certain activity
resistant to change
of or pertaining to pornography that depicts penetration
faster or more intense than the regular style
- broken bricks, stone and/or other aggregate used as foundations especially in road and path laying.
- (music) gangster rap, or thicker, heavier and faster punk or electronic music.
- Let's listen to some hardcore.
Derived terms 
hardcore punk or techno music
broken bricks, stone and/or aggregate