The Blue Book or Enhanced Music CD

Enhanced CD

Enhanced CD, also known as CD Extra and CD Plus, is a certification mark of the Recording Industry Association of America for various technologies that combine audio and computer data for use in both Compact Disc and CD-ROM players....

 specification describes the Enhanced Music CD format. The first session of an Enhanced Music CD contains audio information according to the Red Book

Red Book (audio CD standard)

Red Book is the standard for audio CDs . It is named after one of the Rainbow Books, a series of books that contain the technical specifications for all CD and CD-ROM formats.The first edition of the Red Book was released in 1980 by Philips and Sony; it was adopted by the Digital Audio Disc...

. As a consequence, existing Compact disc players can play back this first Session as a CD Audio disc.

The second session contains CD-ROM

CD-ROM

A CD-ROM is a pre-pressed compact disc that contains data accessible to, but not writable by, a computer for data storage and music playback. The 1985 “Yellow Book” standard developed by Sony and Philips adapted the format to hold any form of binary data....

data files with content often related to the Audio Tracks in the first Session. The second session will only be used by computer systems equipped with a CD-ROM drive, or by special “Enhanced Music CD players”. Today this specification is also called CD-Extra (CD-E).