The Collaborative International Dictionary of English v.0.48:

compact disc \com"pact disc`\, compact disk \com"pact
disk`\(k[o^]m"p[a^]kt d[i^]sk`), n.
   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.

   Syn: CD.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

compact disc
    n 1: a digitally encoded recording on an optical disk that is
         smaller than a phonograph record; played back by a laser
         [syn: compact disk, compact disc, CD]

The Free On-line Dictionary of Computing (30 December 2018):

Compact Disc
CD

    (CD) (Not "disk", this spelling is part of the
   standard).

   A 4.72 inch disc developed by Sony and Philips that can
   store, on the same disc, still and/or moving images in
   monochrome and/or color; stereo or two separate sound tracks
   integrated with and/or separate from the images; and digital
   program and information files.

   The same fabrication process is used to make both audio CDs
   and CD-ROMs for storing computer data, the only difference
   is in the device used to read the CD (the player or drive).

   CD Information Center
   (http://cd-info.com/cd-info/CDInfoCenter.html).

   (1999-06-23)