Yo

Yo is an American English slang interjection. It was highly popularized after being commonly used among Italian Americans and African Americans in Philadelphia, Pennsylvania.

Although often used as a greeting, like the word "hey", it has a wide range of other meanings that depend on the tone, context, and situation.

• "Yo" is often used in the Southern United States as a substitute for the response "Here" to acknowledge one's presence during a roll call.
• "Yo" has also come to be used as an exclamation at the end of a sentence, either to direct focus onto a particular individual or group ("That girl is hot, yo"), or to strengthen meaning to a particular point e.g.: "This hot dog bun is kickin', yo!".

See http://en.wikipedia.org/wiki/Yo