CD-R is an abbreviation of compact disc recordable. Operating on the same premise as a CD, a CD-R is thin disc made of polycarbonate with 120mm diameter used to store music or data. However, unlike conventional CD media, a CD-R has dye core instead of a metal core. A laser is used to etch "pits" into the dye so that the disc can later be read by the laser in a CD-ROM drive or CD player.
There was some incompatability with CD-R and older CD-ROM drives. This was primarily due to the lower reflectivity of the CD-R disc.