Term of endearment, pronounced "bay." Short for "before anyone else." Means the same thing as baby, babe, sweetheart, honey, etc.
I love you, bae.
Shawn: Ay bro you comin with us to the club tonight?
Jamal: Nah man, me and the bae are goin out for drinks for her birthday, I'll meet up with y'all later tho.