To the uninitiated, any loud music is called heavy metal. In reality there are a multitude of heavy metal styles and subgenres. Heavy metal is a wide umbrella characterizing a style of music that is generally loud and aggressive. There are genres that are very melodic and mainstream, and other genres that are extreme and underground. Here's a brief overview of heavy metal and its many styles.
The term "heavy metal" was first used in a musical sense in the '60s song "Born To Be Wild" by Steppenwolf when they referred to "heavy metal thunder." Although there are debates among experts, most consider groups like Black Sabbath, Led Zeppelin and Deep Purple to be the first heavy metal bands. From there the style evolved and branched into many different genres and subgenres. Heavy metal remains a vital force in music today, with sellout concert tours and CDs selling impressive numbers of copies without any radio airplay or MTV exposure.
Musical and Vocal Styles
The backbone of heavy metal is the electric guitar. You can't have metal without at least one guitarist, and many bands have two or more. Certain genres have some quiet and mellow parts, but most metal is loud, intense, fast and aggressive. The vocal styles in heavy metal range from melodic singing to aggressive singing to unintelligible screaming, depending on the genre.
At the beginning there was just traditional heavy metal. Shortly after it evolved and splintered into many different styles and subgenres. This site has a series of articles on many of the genres that will give you a more in-depth look at that particular type of metal. As time has gone on, there are literally hundreds of subgenres, but these are some of the main genres of heavy metal:
Avant Garde Metal
Also called experimental metal, it's characterized by unusual and nontraditional instruments and song structures.
Examples: Arcturus, Dog Fashion Disco, Mr. Bungle, Peccatum, Vintersorg
Characterized by high-pitched raspy vocals and pagan/satanic lyrical imagery. Symphonic black metal is a subgenre that uses keyboards and is more melodic.
Examples: Bathory, Burzum, Emperor, Mayhem, Venom
A combination of heavy metal and Celtic music with lyrics focusing on Celtic mythology.
Examples: Cruachan, Geasa, Waylander
An extreme form of the genre that uses distorted guitars and a growling vocal style sometimes described as "cookie monster" vocals.
Examples: Cannibal Corpse, Death, Deicide, Morbid Angel
A genre that uses slower tempos and emphasizes gloomy, melancholy and atmospheric music. There are numerous subgenres of doom, including drone, epic, industrial, sludge and stoner.
Examples: Candlemass, Pentagram, Saint Vitus, Solstice
A combination of the darkness and melancholy of goth rock with heavy metal. The lyrics tend to be epic and melodramatic. This is a genre that uses a lot of male/female vocal combinations with the male vocalist generally using more aggressive vocals and the female singing in an ethereal soprano.
Examples: Lacuna Coil, Leaves Eyes, Theatre Of Tragedy, Tristania.
This is a genre influenced by thrash metal and death metal. It takes its name from the sound of the atonal guitar riffs combined with blast beats from the bass drum. The vocals are similar to death metal.
Examples: Carcass, Napalm Death, Nasum, Pig Destroyer, Terrorizer
Also called pop metal and hairspray metal, this genre is very melodic and mass appeal. Some of the most commercially successful and critically despised bands came from this genre. They wore a lot of makeup and had huge teased hair, thus the name. They received a lot of radio airplay and chart success in the late '80s and early '90s until grunge rock destroyed it.
Examples: Poison, Ratt, Warrant, Winger, White Lion
This genre is currently very popular and combines heavy metal with hardcore. They use the musical style of heavy metal, especially melodic death metal, and the shouting vocal style of hardcore. Breakdowns are also heavily utilized.
Examples: As I Lay Dying, God Forbid, Killswitch Engage, Shadows Fall
New Wave Of British Heavy Metal (NWOBHM)
This genre has influenced almost all metal that has followed it. These were the metal pioneers that took the original sound of groups like Black Sabbath and took out the rock and blues influences to make the traditional metal sound that we're familiar with today.
Examples: Def Leppard, Diamond Head, Iron Maiden, Judas Priest, Saxon
Combining heavy metal riffs with hip-hop influences and rapped lyrics, this genre became very popular in the late '90s through the early 2000's and then fell from favor. There are a few bands of this style still doing well, although most have come and gone.
Examples: Korn, Limp Bizkit, Papa Roach, Slipknot
A very melodic form of metal that utilizes soaring guitars and strong vocals, usually in a higher register. It's also an epic style, with long songs and many lyrics about mythology, fantasy and metaphysical topics. Most power metal bands also have a keyboardist.
Examples: Blind Guardian, Fate's Warning, Helloween, Jag Panzer
A mixture of heavy metal and progressive rock, this genre utilizes many of the characteristics of avant-garde and power metal. The song structures are complex, using many time signatures and key changes and are usually long. The lyrics are epic and often progressive metal albums are concept albums, utilizing a main theme that runs throughout.
Examples: Dream Theater, Evergrey, Fates Warning, Queensryche
This genre evolved from NWOBHM and became heavier and more extreme. It's characterized by fast guitar and double bass drum with aggressive but understandable vocals. Some of the most popular bands in metal started as thrash bands, although most evolved as they went along.
Examples: Anthrax, Megadeth, Metallica, Slayer
The great thing about heavy metal is that it is continually changing, evolving and improving. Just when you thought it couldn't get any more extreme, something new comes along. Whether you prefer the melody and complexity of power metal or the aggression and intensity of death metal, it's all part of this widely encompassing genre called heavy metal.