A word that is used to replace 'sayonara' ("goodbye") or 'matane' ("see you soon") at the end of a sentence in colloquial Japanese speech. It can be translated into English as "see ya" or "catch ya later".
It is part of the Tokyo Shitamachi dialect and used to be a very popular informal slang expression used primarily by boys and men until sometime ago. Its usage has declined in the past 20 years.
Contrary to what the previous poster has written, it is not necessarily a rude way to say "bye" or only used when you are angry at someone. Although (just like most slang words) if used in the proper context it may be interpreted as being dismissive or sarcastic.
(in typical colloquial Tokyo Japanese):
"Ore uchi ni kairu kara matta ashita na. Abayo!"
Translation: "I am going to go home now so i'll see you tomorrow. See ya!"