MP3 CD is a term used to refer to compact discs (usually CD-R or CD-RW) that contain MP3 files. Discs are burned in data mode (like a CD-ROM), as opposed to Red Book format as with standard audio CDs (CDDA).
MP3s are supported by many modern CD players, including DVD players. There are also CD players capable of playing WMA and Ogg Vorbis files, and on Sony-brand players, audio encoded to their ATRAC format (originally created for the MiniDisc).
Because of this audio data compression, the disc does not have to spin all of the time, thereby saving battery power. The song is buffered in memory, which also provides protection against skipping.
The BBC has released some of its CD back-catalogue on MP3 CDs, including compilations of Doctor Who audiobooks and television soundtracks and the entire Hitchhiker's Guide to the Galaxy radio series (from Amazon). These discs retail at a higher price than typical audio CDs, but contain up to 25 hours of audio on a single disc.
