Hard core

[Tanya Shivari]

having an intense (often excessive) interest in or enthusiasm for some particular activity, pastime or hobby

[Sarah]

A label given to those who are at the top of what they do. Also given to those who have no fear of the consequences of what they do.

[Justin Bieber]

musical attitude or style or genre showing no compromises with approching reality. a direct way of expressing ideas through powerfull walls of sound and an agressive lyric style.

[Tracie Lynn]

a small group of people within a larger group, who strongly believe in the groups principles and usually have a lot of power in it: