A genre of music. More so, a sub-genre of the Rock category that falls between alternative and metal.
Scale from softest->hardest.
Soft rock - Emotional - Alternative - ALUMINUM - Hard Rock - Metal/Death Metal - Screamo.
SOFT ROCK relies on slow melody, and serenity in the vocals. Soft Rock frequently uses intruments that would not normally be used in rock music, like pianos, and acoustic instruments. Soft Rock is praised for its simultaneous simplicity, and complexity.
-Jack Johnson, The Beach Boys.
EMOTIONAL does not require a serene vocalist, but its stress is all vocal, and very little instrumental. Emotional music usually utilizes a vocalist with a high-pitch or "whiny" voice, that is not particularly skillful at pitch, harmony, tune.
-My Chemical Romance, All American Rejects, Saosin.
ALTERNATIVE is very broad, so many bands have been pushed in because they don't have their own genre so they call them "Alternative." Alternative bands qualify as alternative for their earthy vocals and mediocre instrument stress. Most alternative bands rely heavily on their singer to disguise their lack of instrumental talent. Sadly... There is little instrumental stress, usually. Most of the stress is vocal.
-Creed, Matchbox 20.
HARD ROCK employs heavy distorted electrical guitar riffs paired with powerful vocals. The only reservation hard rock has, is screaming. They still sing. Though screaming is not forbidden, and is justified in the movement of the intensity of the song. Aluminum shares this screaming reservation.
METAL screaming can be the norm with no justification. Metal emphasizes solely on shredding a guitar at alarming speed, when necessary, and deemed necessary frequently. Metal songs can last 10 minutes, or more.
-Metallica, Bullet for My Valentine.
DEATH METAL usually forwards a constant raspy demonic sounding vocalist, with skillful guitarists showing the extent of their playing speed and much stress can be placed on the drummer's use of the bass drum, or double bass drum. Death Metal songs can last 10 minutes, or more.
-Lamb of God, Dimmu Borgir.
SCREAMO is purely an assault on one's sense of hearing. They can employ tactics such as "pig squealing" and just outright screaming.
-Job For a Cowboy, Underoath.
ALUMINUM has emotional rooting, so the song has real meaning and definition so it is justified in existing. Then, it has equal instrumental and vocal stress so the song is not imbalanced to mask any lack of talent. The lyrics are powerful, as the guitar/drums are skillful. The vocalists aren't afraid to scream as well as, screaming can be incorporated and still be classified as aluminum WITH justification, normally based on song intensity.
Lyrics are often cryptic, and the tone of the songs can usually be classified as "dark." The tone is not required to be "dark," but it can not be "light" or "whiny." If not "dark" the tone is normally very powerful, elightening, and epiphany inspiring.
Imbalance in instrumental an vocal equality normally disqualifies a song for classifying into the genre.
-Rise Against, Breaking Benjamin, Evansblue, Tool, A Perfect Circle, Chevelle, Skillet, AFI, Incubus.
Daniel: What kind of music do you listen to bro?
Jef: I like some metal shit, but mostly aluminum.
Daniel: Wow, I love you. Rise Against is one of my favorite bands, let us unite in our love for this genre.
Jef: Fuckin' a right dawgie.