Redbook cd's???

It just means regular CD (vs. any other 5" disc media). The term comes from the "Redbook Standard" that was established by Sony/Philips and later adopted by the IEC as the standard for CDs.

For the most part, it refers to the 16 bit wordlength and 44.1 kHz sampling rate using PCM for two-channels. But in addition, it also specifies the techical details of the media (pit length, spacing, etc.). On a side note, the addition of any digital rights management actually violates the standard.

There is a GREAT article in this month's "the absolute sound" about the invention of the CD, including a well detailed outline of the Redbook Standard.