Music that prolly wouldn't be so bad if MTV hadn't gotten a hold of it. The most mainstream (meaning overplayed, and only like by 12 year old fags who think they're hot shit because they can mimic the way 50 Cent and Eminem dress) is cheap beats (made in programs like Fruity Loops Studio) that loop annoyingly, accompanied by a person talking fast about stuff (stupid shit like being a 'gangsta', drugs, sex, women, or their life story. This is the worst form of rap (and I don't mean because of the swears). Underground rap is more closely related to the way original rap/hip hop was recorded, and includes turntablism, sampling, producing, visual art, breakdancing, beatboxing, and more.
It has been said that rap is only hated by rich white people, and blacks only like rap. Not true. I have a black friend who likes rock, I like rock (I am white and not rich).