Thrash metal (or simply thrash) is an extreme subgenre of heavy metal music characterized by its overall aggression and fast tempo. The songs usually use fast percussive beats and low-register guitar riffs, overlaid with shredding-style lead guitar work.

The genre emerged in the early 1980s as musicians began fusing the double bass drumming and complex guitar stylings of the new wave of British heavy metal (NWOBHM) with the speed and aggression of hardcore punk and the technicality of progressive music. Philosophically, thrash metal developed as a backlash against both the conservatism of the Reagan era and the much more moderate, pop-influenced, and widely accessible heavy metal subgenre of glam metal which also developed concurrently in the 1980s.

The early thrash metal movement revolved around independent record labels, including Megaforce, Metal Blade, Combat, Roadrunner, and Noise, and the underground tape trading industry in both Europe and North America. The genre was commercially successful from approximately 1985 through 1991, bringing prominence to Metallica, Slayer, Megadeth, and Anthrax, all grouped together as the "Big Four" of U.S. thrash metal. Other U.S. bands, such as Overkill, Metal Church, and Bay Area acts Exodus, Testament and Death Angel, never achieved the popularity of the "Big Four" but also had considerable success during the late 1980s and early 1990s, particularly on the strength of airplay on MTV's Headbangers Ball. Some of the most successful international thrash metal bands from this era were Brazil's Sepultura, Canada's Voivod, and the genre's "Big Teutonic Four": Kreator, Destruction, Sodom, and Tankard.

The thrash metal genre had declined in popularity by the mid-1990s, due to the commercial success of numerous genres such as alternative rock, grunge, and later pop-punk and nu metal. In response, some bands either disbanded or moved away from their thrash metal roots and more towards groove metal or alternative metal. The genre has seen a resurgence in popularity since the 2000s, with the arrival of various bands such as Bonded by Blood, Evile, Hatchet, Havok, Lamb of God, Municipal Waste, and Warbringer, who have all been credited for leading the so-called "thrash metal revival" scene.