Experimental Metal

Experimental metal, also known as avant-garde metal or avant-metal, is a subgenre of heavy metal music loosely defined by use of experimentation and characterized 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. It evolved out of progressive rock, jazz fusion, and extreme metal, particularly death metal and black metal. Some local scenes include Los Angeles and the San Francisco Bay Area in the United States, Oslo in Norway, and Tokyo in Japan. Pioneers of experimental metal include Boris, Celtic Frost, Earth, Helmet, Maudlin of the Well, Neurosis, Sunn O))), and Voivod.

Source: http://en.wikipedia.org/wiki/Experimental_metal