Juvenile version of New England adjective "Pissah" when your mother wouldn't let you say bad words. Means "great" or "awesome". Derived from "pissah" and "whiz" in use by children.
A simpler way to say nigger or nigga, sort of originating from TFE and "izzle" talk, such as nizzle.
Not really derogatory, just a playful and mentally illalternative to nigga.