What music is classified as dubstep? Only heard of the term recently

When I look up dubstep, I hear these two kinds of sounds, one very heavy electronic and screaming, and the other much more toned down with deep bass sounds. Are these both considered dubstep? Are they different styles of it. I was recommended this music style by a friend and I've never heard of it before. I'm not sure I enjoy it but it's surely interesting and unique.