Any Optical disk of a variety of information storage disks that are played or read using a bluray or laser . Optical disks include compact discs (CDs and CD-ROMs), laser discs, and digital versatile discs (DVDs and DVD-ROMs). WORM (Write Once Read Many) disks can be used to record data, but once data is recorded it cannot be altered except by obliterating the old version and storing the new version on a previously unused portion of the disk. Data or sound may be recorded to and erased from any portion of a magneto-optical disk multiple times. Magneto-optical disks, such as the rewritable optical disk and the recordable disk used with the Mini Disc player, have a special layer, as of barium ferrite, that can be magnetically polarized by a recording head when heated with a laser.