Redbook is the 1980-defined standard fro Audio CDs.Â  It defines CD audio as 44.1khz, 16-bit linear PCM-encoded audio, with a number of parallel tracks called P, Q, R, S, T, U, V and W which encode various bits of data useful to the CD.Â  P and Q codes in particular handle things like â€œtrack startâ€ and â€œtrack end.â€
Thereâ€s also â€œorange bookâ€ and â€œyellow bookâ€ and a few other colors used for defining other CD standards, like CD-ROM, CD+G, etc.