Comes from the words "Hey, yo" which eventually evolved into the one word, "Aeo".
By dropping the H, and putting the Y's together, it looked like 'eyo' which was pronounced "Ay Oh" and was simply spelled the new way, A E O.
Bouyo isn't ment to mean anything other then to represent the person being spoken to.
Amber: Because she's in AEO. Wow i'm jealous, she's amazing.
Sally: You're right, i wish we were as amazing as them.