Avant-Garde, also known as Experimental Metal, is a subgenre of heavy metal music characterised by the use of innovative, avant-garde elements, large-scale experimentation, and the use of non-standard and unconventional sounds, instruments, song structures, playing styles, and vocal techniques. Though there is no convention or criteria to exactly define the genre, some experimentation in the music is generally a major criteria to define the genre. Avant-garde metal is related toprogressive metal, but avant-garde metal often has more experimentation, while progressive metal usually has a tighter focus on traditional metal instrumentation and higher levels of technical complexity. Avant-garde metal also uses unusual sounds, breaks conventions, and often includes new elements. The lyrics and visual presentation of the genre are eclectic as well. It has been called the most difficult heavy metal genre to define and describe, but it has been defined by integrating a wide variety of music like jazz and fusion added to aggressive music styles such as black metal, and keyboards are widely used to create atmosphere. Usually avant-garde metal bands fall under another genre of music as well, as the term is similar to extreme metal in how it is a loose term covering a wide variety of bands. The term "experimental metal" is often referred to as "atmospheric metal", although in this usage the terms describe "Post-Metal, in reference to Post-Rock.
According to Ian Christe, avant-garde metal emerged out of death metal as a number of musicians "Abandoned the tightly wound structure of the music and experimented with abstractions of its founding elements."[ Major pioneers of the genre include Celtic Frost, Voivod, Sunn O))), Fleurety, Ved Buens Ende, and Maudlin of the Well. Most of these bands were part of the early black metal or progressive metal genres, or both. Two record labels which promote avant-garde metal are Holy Records and The End Records. Prominent regional scenes include the United States, with bands like Agalloch, Maudlin of the Well, Naked City, and Psyopus, and Norway, with bands like Age of Silence, Arcturus, Ram-Zet, Ulver, and Ved Buens Ende. Also, in the United States, a local avant-garde metal scene has emerged in the San Francisco Bay Area with bands such as Giant Squid, Grayceon, and Ludicra.