Emo was really a "trend" or whatever - mostly teenagers wearing black, tight fitting clothing, lots of eyeliner (for guys as well) and specific hairstyles, mostly where the fringe goes over one eye, slightly to the side
it was meant to be about the kinad music they listened to (whiny "emo"tional indie or screamo stuff), but was more about the fashion really
so because of the whining, people now refer to emo as being people who moan about their lives without doing anything about it, feel sorry for themselves etc