A bastardized term that is by most of the population thought to mean "for sure" or any number of agreements. The true meaning, however, is "I concur with you whole heartedly my fellow African brother."
Ghetto black man: "Fo shizzle my nizzle!"
Rich black man in response: "I concur with you whole heartedly my fellow African brother."
Ghetto black man: "..."
For sure, definitely, no doubt ... emanating from the "iggity style" language made popular by the Double Dutch Bus song, Das EFX and brought back out by Snoop