Metalcore

Metalcore is a subgenre of Heavy Metal that combines Thrash Metal with Hardcore Punk, and sometimes takes a more melodic approach to the songs than thrash. It is characterised by gratuitous use of the Metal Scream, as well as breakdowns. Lots and lots of breakdowns (although due to, ahem, certain bands, this attribute has been Flanderized a bit). If you're not in the know, a "breakdown" is when the music kind-of slows down to induce moshing or "throwing down"...or something like that. Modern bands often tend to mix it up with clean vocals and melodic riffs (see Melodic metalcore below).

Metalcore began life as a blending between thrash metal and hardcore punk, and was used to describe bands such as D.R.I., S.O.D., and Suicidal Tendencies in the 1980's, however the term changed its meaning in the 1990's to "metallic hardcore", and the genre metalcore originally defined became known as "crossover thrash". This newer "wave" of metalcore included bands such as Integrity, Earth Crisis and Converge. By the end of the nineties, metalcore had evolved into "melodic metalcore", which slowly grew in popularity until the mid-2000s, when it was a big mainstream draw. In fact, today, metalcore is the most commercially popular form of metal.

When combined with Death Metal, metalcore transforms into Deathcore. Melodic metalcore is usually fused with Melodic Death Metal influences and Soprano and Gravel vocal dynamics.

Bands typically cited as Metalcore include:

The Acacia Strain
A Life Once Lost
The Agonist
All That Remains (their first album was melodeath)
As I Lay Dying
Asking Alexandria
Atreyu (early)
Attack Attack! (Combines this with post hardcore and electronic music, sometimes called Electronicore)
August Burns Red (Also considered Progressive Metal)
Avenged Sevenfold (early; later became Heavy Metal / Hard Rock)
Between the Buried and Me (also a Progressive Death Metal band, so Your Mileage May Vary as to how much they belong in this subgenre)
Botch (Trope Maker/Ur Example for mathcore along with Converge)
Bring Me the Horizon (started off as deathcore)
Bullet for My Valentine
Caliban
Candiria (mixed with Jazz Fusion and Hip Hop)
Cave-In (Earlier work, some of their later material is more Alternative Metal)
Chimaira (mixed with Groove Metal)
Converge (Trope Maker for mathcore)
Curl Up And Die
A Day to Remember (often leans toward Hardcore Punk and even pop-punk)
Demon Hunter (somewhat blurs the line between metalcore, nu-metal and Groove Metal; as with Between the Buried and Me, Your Mileage May Vary as to whether they count)
The Devil Wears Prada
The Dillinger Escape Plan (they are part of the sub-genre, Mathcore, so their sound somewhat differs from traditional Metalcore fare)
Earth Crisis
God Forbid (likely the least hated example; also falls under Thrash Metal)
Haste the Day
Hatebreed
HORSE The band (Also Nintendocore)
In This Moment
Integrity
Killswitch Engage
Lamb of God (Your Mileage May Vary; they're not very melodic, and possibly closer to Groove Metal or Thrash Metal, plus the metalcore hatedom is desperate to find some criteria to exonerate them)
Of Mice and Men
Overcast
Parkway Drive
Poison the Well
Protest the Hero
Psychostick
Sea of Treachery
Shadows Fall (mostly Thrash Metal; YMMV as to if they count)
Straight Line Stitch
Trivium (influences also drawn from Thrash Metal and Melodic Death Metal for more recent albums)
Underoath
Unearth
Walls Of Jericho
The Word Alive
Zao

The following bands are often called metalcore, but are very much not metalcore. We keep this short list here because we don't want these bands put on the main metalcore list by an earnest passerby.

3 Inches of Blood: The confusion comes from the dual vocalists. While switching between clean, punk styled vocals and harsh, growled and screamed vocals is common in metalcore, 3 Inches of Blood is very much a thrash-power metal band with little to no similarities to metalcore outside of common thrash elements. Furthermore, while one of their vocalists does use similar screams to some metalcore bands, their other vocalist uses a Halfordesque screech that's far more in line with thrash metal, speed metal and Power Metal.
The Black Dahlia Murder: Straight-up Melodic Death Metal.
DevilDriver: Straight-up Groove Metal.
Five Finger Death Punch: Straight-up Groove Metal on their first album, thrashier groove metal along the lines of Pantera's faster songs on the second. Some of their mellower songs border on Post-Grunge.
Light This City: They mostly look like hardcore kids, and the other bands they've been in are mostly hardcore or pop punk, but the music is straight Melodic Death Metal.
Soul Embraced: Possibly due to being a Christian band. They started out as a straight up death metal band, but their later albums brought Progressive Metal and Alternative Metal influences into the fold.

Metalcore provides examples of the following tropes:

Christian Rock: Metalcore and Post-hardcore are both filled with Christian bands for whatever reason. Most famously are The Devil Wears Prada, Underoath and August Burns Red.
- Not Christian Rock: They also have a bunch of this
Fan Dumb: While most metalcore fans are perfectly fine, there's still at least one person on Facebook, YouTube, or some other site that's going to put down people putting down the band in question - typical comments include mentions of wealth and talent or jealousy on the Hatedom's part.
Gateway Series: To Extreme Metal
Heavy Mithril: Averted most of the time.
Lighter and Softer: Than other Extreme metal genres, usually.
Hatedom / Hate Dumb: Due to its immense popularity and the fact that it is sometimes perceived as a form of Hardcore Punk rather than Metal by metalheads, the genre has accumulated a rather large one of these.
Mohs Scale of Rock and Metal Hardness: Usually about an 8 or 9. Occasionally dip down to a 7 (All That Remains does this sometimes) or very rarely go up to a 10 (Chimaira being an example of a band that does this). Converge and a couple of other groups sometimes go Up to Eleven, but this is pretty uncommon.
Neoclassical Punk Zydeco Rockabilly: Most metalcore brings in alot of influences throughout the extreme metal scene, mainly Melodic Death Metal, Death Metal, Black Metal, and Thrash Metal. Some bands bring in influences from Pop Punk, Electronic Music, Groove Metal, and Alternative Metal.
Scary Musician, Harmless Music: Commonly inverted. They usually dress like an average person or androgynously, but the music is still fairly heavy metal.
The Scrappy: some metalheads seem to think so, but it still has a large fanbase
Soprano and Gravel: Most bands have this. This unfortunately causes people to assume any metal band that uses this dynamic is metalcore. Melodic Death Metal (and even regular death metal in some cases) are the usual victims of this.
Surprisingly Gentle Song: Almost every band on this page will have at least one of these per album.
Wangst: Occasionally