Thrash metal is a subgenre of heavy metal music, one of the extreme metal subgenres that is characterise by high speed riffing and aggression. Thrash metal songs typically use fast, percussive and low-register guitar riffs, overlaid with shredding-style lead work. Thrash song lyrics sometimes express views which prefers to attempt an objective critique of society. Thrash metal lyrics also often deal with social issues using visceral and blunt language, an approach which partially overlaps with the hardcore genre. The so-called "Big Four" of thrash metal are Slayer, Megadeth, Metallica, and Anthrax, who essentially simultaneously brought fame to the genre in the mid 1980s.