1) (n) Totally dope, incredibly fine. Probably orignated from the "Boo-yaa Tribe". That shit was straight-up boo-yaa" -- ??.
2) (n) Impression of the sound of a shotgun, also "boo-yaaka". "Shotgun goes boo-ya" -- Cypress Hill (Hand on the pump 1993
3) (n) Marijuana, probably derived from Buddha.
4) (n) Crack, probably related from the fact that smoking crack is sort of equivalent to putting a shotgun to your head and pulling the trigger.