But since you asked, emo is a subgenre of indie/punk rock music, with a heavier focus on melody and emotional lyrics. Catagorizing emo can be dificult, because no bands actually admit to being emo.

A group of white, mostly middle-class well-off kids who find imperfections in there life and create a ridiculous, depressing melodrama around each one. They often take anti-depressants, even though the majority don't need them. They need to wake up and deal with life like everyone else instead of wallowing in their imaginary quagmire of torment.
Emo conversation!
XxSlavetoAnguishxX: omg my gf just left me
acidburnedsoul: that sux man
XxSlavetoAnguishxX: i blame myself only i'm such an ass *cries*
acidburnedsoul: dude come over to my house and we can cut ourselves together
XxSlavetoAnguishxX: okay *cries*
acidburnedsoul: omg dashboard confessional has a new cd, i preordered it already
XxSlavetoAnguishxX: dude they're my favorite band to self-mutilate to
acidburnedsoul: i prefer to cut myself while watching Napoleon Dynamite on my bigscreen
XxSlavetoAnguishxX: dude that movie is so deep. i cry every time i see it
acidburnedsoul: me too. i hate myself
XxSlavetoAnguishxX: yeah we're such tortured souls, nobody understands how hard life is for us
acidburnedsoul: yeah we got it tough dude. pass the tissues