Abbreviation for "for straight for shizzie" AKA "for straight for shizzle."
This is commonly used as a fancy way to say 'hell yea' or 'no doubt.' Basically, acknowledging a comment while also adding a sense of excitement or anticipation.
kid1--> what we doin' tonight?
kid2--> We gonna go to the party tonight, get crunk, and nail us some hotties.