Stating that you are "for sure" going to do something. It is definate and without a doubt (that is why it is stated twice in a row).
Known from the character Seth in the popular teen movie Superbad, where he tells Jules that he will "for sure" buy alcohol for her party.
"Yeah we're going to the party fo sho fo sho. We're going to the party fo sho."
a girl (or guy i suppose) that is known for being easy. So easy, in fact, that you will "for sure" ("fo sho") be getting laid by them. Also known as a slut.
Dude, i'm so stoked to go out with Suzy tonight; she's a fo sho fo sho!