Wiktionary
n. (context music English) A subgenre of hip-hop music with horror-themed lyrics and imagery.
Wikipedia
Horrorcore is a subgenre of hip hop music based on horror-themed and often darkly transgressive lyrical content and imagery. Its origins derived from hardcore and gangsta rap artists such as the Geto Boys, who often incorporated supernatural or occult themes into their lyrics and, unlike most gangsta rap artists, pushed the violent content and imagery in their lyrics beyond the realm of realistic urban violence to the point where the violent lyrics became gruesome, ghoulish, unsettling, or slasher film-esque. The term horrorcore was popularized by openly horror-influenced hip hop groups such as Flatlinerz , Gravediggaz & Da Lench Mob