Alternative metal is an eclectic form of rock music that gained popularity in the early 1990's alongside grunge. In many instances, it can be accurately described as a fusion of heavy metal and alternative rock, especially the indie rock of the 1980's. It is characterized by some heavy metal trappings (most notably heavy riffs), but usually with a pronounced experimental edge, including unconventional lyrics, odd time signatures, unusual technique, a resistance to conventional approaches to heavy music, and an incorporation of a wide range of influences outside of the metal music scene.
The term is used as a very loose categorization, but is usually used to describe artists playing a style of metal which is considered either a unique approach to metal music or difficult to define as strictly metal or alternative. Faith No More is a good example of a band in which both criteria apply.
Heavy metal is an essential component of the music, but it was very different from the thrash underground of the 1980s. Initially alternative metal appealed mainly to alternative rock fans since virtually all 80s alt-metal bands had their roots in the American indie underground scene. Alt-metal bands commonly emerged from hardcore punk (Corrosion of Conformity), post-punk/gothic rock (Jane's Addiction), noise rock such as the "pigfuck" sound of Big Black and Sonic Youth (Helmet, White Zombie), grunge (The Melvins, Soundgarden), industrial music (Ministry, Nine Inch Nails), and other mov...
A form of alternative rock music which pretends to be metal music due to some metal influenced riffs. This genre is considered to be metal for people who can't handle anything heavier than Breaking Benjamin.
Person 1: I was listening to some Breaking Benjamin. Are they metal or rock?
Metalhead: They are alternative metal music. They are too wimpy to play real metal, so they play alternative rock pretending to be metal.