A subgenre of metal and hardcore that is kind of like communism. If it were to be done correctly, it would be perfect, but hardly anyone can do it right and therefore it is mainly horrible. There are some metalcore bands that I actually enjoy (The Dillinger Escape Plan, Hatebreed, Every Time I Die), but most of it (and certainly the most popular bands) incorporate pop punk, electronic, glam, crunk, and all sorts of other shit and make it sound worse than putting a cat in a blender. Not to mention deathcore, which is just an attempt to make an anti-metalcore genre, is even worse and brings shame to death metal. Another thing that humor's me with most metalcore is the bands claim to be the brutalist shit alive but they dress like a 12 year old scene girl.
Good metalcore: Every Time I Die, TDEP, Hatebreed, All That Remains (sort of), ect.
Bad metalcore: Bring me the Horizon, Of Mice and Men, Asking Alexandria, The Black Dahlia Murder, Chelsea Grin, ect.