Hardcore can be used to describe a number of genres including:

1) The genre of hardcore punk as well as its various offshoots and derivatives. It can also be used as an adjective rather than a genre, often to describe a metalcore band that sounds heavier or more "hardcore" than other bands, the hardcore scene often uses "hardcore" to describe metal derived music that is more inclined towards being "moshable".

2) A genre of electronic music, with has some characteristics like being harder than the other electronic music genres and the songs having higher bpms, sometimes called hardcore techno or gabber.

3) The genre of Hardcore Rap or Hardcore Hip Hop.