Compact Discs, commonly referred to as CDs, are a type of optical disc storage media format that was first released in 1982. CDs are used to store digital data, such as audio, video, and computer programs. The term 'compact disc' is derived from the fact that the discs are much smaller than traditional vinyl records. CDs are made up of a polycarbonate plastic disc with a thin aluminum layer on top. The data is stored in the form of microscopic pits on the aluminum layer. The pits are then read by a laser beam, which is reflected off the aluminum layer and onto a photodiode. The data is then converted into an electrical signal and sent to the CD player. The answer to the crossword puzzle is MIRRORS, which is a reference to the reflective aluminum layer on the CD.