Green’s Dictionary of Slang

(US campus) a greeting, hello.

1947		M.H. Boulware Jive and Sl. n.p.: What you know, Joe? ... Good morning.
1965		B. Jackson Get Your Ass in the Water (1974) 123: Now they’ll set you down in their parlor and ask you, ‘Boy, what you say?’.
1997		C. Newland Scholar 27: ‘Wha’ you sayin’ man?’ he beamed up at them. ‘Cool star, I’m safe.’.
2000		(con. 1940s–60s) Décharné Straight from the Fridge Dad.