There were a few thing synonymous with heroin chic. One was the makeup, it was very dark eyes, pale skin, almost dirty looking but not quite.
Then of course, the body of heroin chic was, as your best friend said, very skinny. Small breasts, kind of frail looking....just very skinny and gaunt.
Kate moss infamously started the "waif" look when she came on the scene in the early 90's, which grew into the heroin chic trend of the early to mid nineties......
Honestly I don't think Kate Moss was all that much skinnier back when she started then she is now. She was really young when she first came out so her body probably developed more, but she's still skinny, it's just how she's built.
the name heroin chic basically came from the drugged out appearence of the models. It originally started at the same time as the grunge movement in music, which was also very dark and seedy so the two trends really worked together, but heroin chic outlasted grunge by a few years.