CD's, or 'Cock Dribble's', are a collection of the sounds people make when they are ejaculating badly. These are in disc format, and can be played in stero systems or computer, or converted to mp3 and stored on your iPod etc.
Another reference to when two dudes try to stuff both of their man meat into a chick's pussy. I'm not sure where the origin came from, but I heard the term used on Eminem's response to Mariah Carey's "Obsessed".
"...When me and Luis were tryin to stick two CD's in the same slot."