a) short for the term emotional...in a musical sense
b) music derived in the 80's... with such bands as Rites of Spring, Texas is the Reason, and more.
c) can be used to describe a person who listens to emo, can relate to most of it and then cry because they can relate to it and not just because its emo.
emo music is not punk.
emo music usually contains lyrics which have a desperate side to them. written usually about a past girlfriend or experience.