Hatecore - an alternative word for RAC (Rock Against Communism) bands.
Discore - anything that sounds like the seminal punk band Discharge.
Norsecore - Norwegian Black Metal. Vaguely insulting, since the old NBM motto was "No Mosh, No Core, No Fun, No Trends".
Queercore - a term used by the outrageously camp pop-punk band Pansy Division.
Hardcore - a large-grained gravel used to provide a solid but porous bed beneath, for example, a driveway. Not using hardcore or distributing it badly will almost certainly lead to subsidence.
Mallcore - a disparaging term for nu-metal, based on the notion that most of its fans are keychained mall-rats.
Rapcore - a slightly less derogatory term for nu-metal, used mostly when it focuses more on rapping than on bonehead riffs.
Metalcore - thrash played by skinheads.
Deathcore - death metal played by skinheads.
Punkcore - a completely pointless term in theory, in practice it differentiates so-called "real" punk (with a small r, since Real Punk is an early name for Discore) from pop or skate punk on the one hand and from the rigid hardcore scene on the other.
Grindcore/Crustcore - Extremely noisy punk rock with guitars that sound like they're "grinding" rather than playing music.
Noisecore - broadly speaking, anything loud that a metal journalist can't classify. Usually featuring a multitude of riffs, time changes and headspinning musical devices, with screamed vocals.
Mathcore - A usually derogatory term for over-technical noisecore, focusing on having lots of absurd time changes rather than being any good.
Carcrashcore - the logical extension of noisecore, where the object is to stuff as many genres as possible into a song sequentially and make even less sense.
Digital Hardcore - anything that sounds like Atari Teenage Riot. Punk rock mixed with gabba and IDM elements.
sXecore - literally "straight-edge-core". Hardcore or metalcore written by militant vegans.