Can someone explain to me exactly what dubstep is? Like, what makes a song fall into the dubstep genre?

I've listened to a fair amount of stuff labeled dubstep, including the song linked in the first post of this thread and...it just sounds like obnoxious techno. I mean, is that all dubstep is? Why is it called dubstep? What sound is it that's separating it from other techno/house music?

Someone enlighten me please.