Thrash metal (sometimes referred to simply as thrash), is an extreme subgenre of heavy metal that is characterized by its fast tempo and aggression. Thrash metal songs typically use fast, percussive and low-register guitar riffs, overlaid with shredding-style lead work.Thrash metal lyrics often deal with social issues using visceral and blunt language, an approach which partially overlaps with the hardcore genre. The "Big Four" of thrash metal are Anthrax, Megadeth, Metallica and Slayer, who simultaneously created and popularized the genre in the early 1980s. *source : Wikipedia More Details : http://en.wikipedia.org/wiki/Thrash_metal http://en.wikipedia.org/wiki/Speed_metal