1) A contraction of the possessive prenominal adjective "your."
2) An informal address or title to one whose name is not known to another; can be used as an interrogative address.
3)A declaritive or imperative exclaimation, whether alone or within a sentence.
1) How's yo momma?
2) Hey, yo! What's up, yo?
3) Yo! What the hell do you think you are doing?! Yo, just do your job! YO!