I have a question about burning CD's?

I would like to know what is the original format for music files on CD's. Its something I am not familiar with, but I am doing this as a favor for a friend of mine. They would like a CD that would be able to be played on a Pioneer 12 disc CD changer, thats not MP3 format. I have no clue as to what format songs are on CD's are originally MP3 or WAV.I just know that WAV, are smaller files than MP3's thats all I know about that. Can someone please help me out with this, thanks.