compact disc

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A small optical disc on which data such as music, text, or graphic images is digitally encoded.

from the GNU version of the Collaborative International Dictionary of English.

• noun 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An optical disc used to store audio or other data.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a digitally encoded recording on an optical disk that is smaller than a phonograph record; played back by a laser