Also, within music and audio engineering, a lot of the time the vocals (anything to do with voices) will be referred to as "vox".
For example, if a band is recording a song, they could say: "We've recorded all of the music for our song, now we just need to record the vox."
But like everyone else said, I don't really hear the word "vox" used very much, except for in those very specific situations :)