I would be VERY impressed to see one individual, using the common English language*, not colloquialism or slang, define each of these elements as separate a entity:
metalcore
deathcore
grindcore
death metal
black metal
prog metal
neumetal
- in descriptive individual terms, that have specific, definitive elements to that genre'.
* By that I mean that instead of saying "sick shredding", use commonly understood terms such as "very fast transitions or extremely fast fingering or cords". If something cannot be defined by anything but slang, that definition by default is not exacting.
Keeping in mind that they all hold similarities to each other due to all of them being "Metal"
Here is how I, In my humble opinion, define these:
metalcore- A subgenre primerally consisting of a relatively heavy atmosphere, an agressive mix of clean and screamed vocals with more of a rock or soulful singing style. While still portraying an obvious melody. Many of the songs are often about love. Very popular, many mainstream metal bands do this Ex. All that Remains, Killswitch engage.
deathcore- A more dark subgenre, often seldom using clean vocals but with an obvious intended instrumental melody. Vocals are more of a heavy chant. Focusing on more agressive fighting related themes and portraying an angry atmosphere. Lots of energy.
grindcore- Sungenre primerally consisting of a very technical and quick atmosphere. Guitarists and especially the drummer are playing at very quick tempos, with very fast drum kick speeds almost making a drone-like atmosphere. Vocals are primerally screamed in the higher register. Stops, starts, and instant tempo changes are exemplified in this genre. Malodorus for example.
death metal- Possibly the most aggressive of the given subgenres, portaying a theme of blood, murder, and death. Often a consistant barrage of heavy guitars and a very thick atmosphere of the music. Vocals are generally very gutteral and demonic The song has a very simple undebeat. Good headbanging music. Cannibal corpse for example.
black metal- Consisting of a very drawn out atmosphere and instrumental work, with a constant drive throughout the song. Themes of war, glory, adventures, fantasy, battles ect. Often high pitched vocals, keyboards and orchestral sounds implemented. Often in strange attire and makeup for the stage show.
prog metal- Metal mixing many genres and styles, song often transits from from section to another, rather than completely stopping. Music tends to be complex and extreme on the senses, many time signature changes are often used, usually with drawn out solos of some form. This genre is hard to define given that near "anything goes" as far as themes, styles, vocals, and melodies are implemented. Often other metal genres will be used, with ambiance, funk, rock, country, or other music genres head within the epoch. Ex. Between the Buried and Me, Opeth, Dream theater.
neumetal- Metal consisting of a generally rough and fight-like attitude. But supplementing itself with hip-hop, pop, or other mainstream influences to creat it's sound. Vocals are often sung or chanted rather than screaming, but screams are implemented. Metal creating more of a pop or hip-hop style of rhythm. Disturbed and Korn being being the first two that come to mind.
There you go, I may be off a bit, but that is how I tend to think of it. When it gets down to the nitty gritty of subgenres its often a little subjective. Regardless, that is MY opinion and definition of the subgenres. To each his own.