A CD-R (Compact Disc-Recordable) is a variation of the Compact Disc invented by Philips and Sony. CD-R is a Write Once Read Many (WORM) optical medium, although the whole disk does not have to be entirely written in the same session.
CD-R retains a high level of compatibility with standard CD readers, unlike CD-RW which can be re-written, but is not capable of playing on many readers.
Read more about CD-R: History, Physical Characteristics, Speed, Writing Methods, Expected Lifespan, Labeling