EMO - is more fashion than anything else, the fashion is mainly wearing black, jet black hair (covering half the face), lip piercings, eyeliner. Sadly emo get stereotyped to being kids who sit and cut themselves which is crap. That is NOT emo thats just a sad thing called depression (get help!) and infact many "emos" disagree with self mutalation completely. Emos are said to be moody, dark and have bleak outlooks on life but most are happy and comfortable with their own styles.
Many bands are also considered to be emo such as My Chemical Romance, From First To Last, Hawthorne Heights, 30 Seconds To Mars etc as they sing on moody and sometimes death related themes.
Last note, dont judge or stereotype "emo" people especialy if you dont know them. You wouldnt want someone to judge you.
An "emo" guy might wear - black skinny jeans, black "band name hear" t-shirt, hair in his face, eyeliner.