A word who's origin is made to be puzzling, but is really made famous by the Movie "Rocky" and by various rappers. Yo is a word deeply connected in the Philadelphia culture, therefore; no, it is not used only by "little black kids" or "wannabe suburbans" like the definitions before it has stated.
A history lesson about the word's popular use in Philly from the New York Times:
"In the 1930's a large proportion of the residents of South Philadelphia were Italian immigrants, mostly from the Campania region of southern Italy, the principal city of which is Naples.
In the Neapolitan
" (pronounced guahl-YO-nay) signified a young man. The chiefly unlettered immigrants shortened that to guahl-YO, which they pronounced whal-YO. That was inevitably further shortened to yo. The common greeting among young Italian-American males was "Hey, whal-YO!", and then simply, "Yo!" And so it remains today."
Sorry for this long post, but I had to handle my business
about my city.
And the "Yo" is the pronounciation of the word "you're," is usually spelled yo'.
"Yo man, that jawn
was hot yesturday
"Yo, I can't believe they ran out of cherry wooder ice
"Yo! Come here!"