Used variously to attract attention, greet someone, introduce or emphasize a remark, etc.
Webster's New World
Used to express emphasis.
Today's my birthday, yo.
(slang) A greeting similar to hi.
Yo Paulie! How's it going?
(slang) An interjection similar to hey.
Yo, check this out!
(colloquial) Shortened form of your.
Yo sandwich only has bacon in it. Want some ketchup on that?
(Baltimore) Third-person singular, familiar.
Yo was tuckin' in his shirt! (Stotko and Troyer 2007)
Yogyakarta, a special region of Indonesia.