Beso really means a sloppy, drunk bitch. But it can be used to mean slut or ho, too. For the most part, a beso is a party girl who is out of control. It can be used playfully between friends, but if you say it about someone you don't know it could be taken as fighting words.
The word beso originated in Albany, New York.
Paris Hilton is an example of a Beso.
You could say: "What up Beso!" to your girl.
Or you could see some complete trash thatt you can't stand and wisper to your girl: ..."mega Beso"