Yo is a word that came from Egyptian times, and most people over the age of 50 probably haven't ever heard of it before. It came from the word yo-yo which came from the word llama.
In other langauges Edit
In Japan it means f*** you. In China it means f*** me. In Korea, it means go f*** yourself. In Russia, it means go f*** someone other than you or me.
See also Edit