What is the meaning of the word "hard-core"?

Definitions:

  1. extremely explicit copy to clipboard adjective
    • hardcore pornography copy to clipboard
  2. intensely loyal copy to clipboard adjective
    • Their hardcore supporters thought they had given up their ideals. copy to clipboard
  3. stubbornly resistant to change or improvement copy to clipboard adjective
    • hardcore addicts copy to clipboard

Synonyms: