It’s a genre or subset of electronic music, often consisting of a BPMs around 70–90, bass heavy, often “wobbling” synthesizers, and is generally based around a buildup leading to a “drop”, where the song changes and goes to a second, usually more intense part.
I think most of the people that hate on dubstep are the same ones that call the entire electronic genre “techno”. No offense to anyone here, but if you don’t like music made with sequencers, computers, or synthesizers, you’re not going to like dubstep, and you probably won’t think it’s even “real music”.
That being said, I’m pretty okay with dubstep. There’s genres of electronic that I certainly prefer, like drum & bass or big beat, but the old dubstep out of London, before the genre got huge with Americans, is some of the neatest and most innovative music I’ve heard.
Granted, there is so much dubstep out there that is just genuinely terrible, but so much of it is really good. And to me, it’s gotten people who normally would hate electronic music into it, into much, much better genres such as glitch or drum & bass.