A spanish slang word, usually of Mexican
dialect. Masculine noun.
It means either "homeboy" or "bro." A very friendly term to refer to your amigo.
An example: "Oye ese! Que hay de nuevo?" ("Hey there, bro, what's up?")
It's in a couple of movies like Desperado, and in "Insane in the Brain" by Cypress Hill. When you hear it in the opening of the song, you wonder what it is, especially since you can't find it in a regular dictionary.
There's a really good Spanish Slang dictionary over at: