Cool way of saying "for sure"... even cooler than "fa sho" or "fa shizzle".
Yo, you tryna' come to Applebee's with us?"
-Fo' shillz."
or...
"Yo, did you fuck that bitch last night?"
-"Fo' shillz."
Friend: Are you going to the mall?
Other Friend: Fo Sho
To check somethin in the affirmative
Niglit 1: yo bro i just found a tenner on the floor
Niglit2: fo' Cereals!??
Niglit1: yeah yeah fo cereals!
A slang. Another way of saying "For sure".
Guy one: Hey boss, can I get a pizza pleaz
Boss one: Fo So