CDDB, short for Compact Disc Database, is a database for software applications to look up audio CD (compact disc) information over the Internet. This is performed by a client which calculates a (nearly) unique disc ID and then queries the database. As a result, the client is able to display the artist name, CD title, track list and some additional information. CDDB is a licensed trademark of Gracenote, Inc.
The database is used primarily by media players and CD ripper software. If a CD is not recognized by a media player or CD ripper it can be added to the database if the user fills in the names and artists etc. in a media player such as iTunes or MusicMatch Jukebox.
The need for CDDB is a direct consequence of the original design of the CD, which was conceived as an evolution of the gramophone record, and did not consider the audio tracks as data files to be identified and indexed. The audio CD format does not include the disc name or track names, so a supplemental database is needed to supply this information when discs are used with modern media systems. A later development called CD-Text is another solution to the same problem.
Read more about CDDB: History, How CDDB Works, Example Calculation of A CDDB1 (FreeDB) Disc ID, Classical Music, Alternatives