a disk-shaped optical data storage medium approximately 4-3/4 in. in diameter, which stores binary data as microscopic nonreflective holes or pits in an otherwise reflective surface, and is recorded and played back by rotation in an electronic device containing a laser. It is often referred to by its abbreviation CD. It is a type of optical data storage medium. Compact disks are used for recordings of music as well as of data for computer applications.  [WordNet 1.5]