Thrashcore (also known as fastcore) is a fast tempo sub-genre of hardcore punk that emerged in the early 1980s. Thrashcore is essentially sped-up hardcore punk, with bands often using blast beats. Songs can be very brief, and thrashcore is in many ways a less dissonant, less metallic forerunner of grindcore. Like hardcore groups, thrashcore lyrics typically emphasize youthful rebellion or antimilitarism. In some ways, the genre is aligned with skateboarder culture.

Thrashcore is often confused with crossover thrash and sometimes thrash metal. Further confusion is added by the fact that many crossover bands, such as D.R.I., began as influential thrashcore bands. The term thrashcore is of recent vintage but dates from at least 1993. Throughout the '80s, the term "thrash" was in use as a synonym for hardcore punk (as in the New York Thrash compilation of 1982). It eventually came to be used for the faster, more intense style pioneered by D.R.I., just before their crossover period. The "-core" suffix is necessary to distinguish it from the thrash metal scene, which is also referred to as "thrash" by fans. Still more confusingly, the term "thrashcore" is occasionally used by the music press to refer to thrash metal-inflected metalcore.