Very recently new icons were added that are meant to represent optical drives.
Unfortunately the new identifiers for these refer to them as "disk" when they should be "disc". Convention in the computer industry is to use "disk" when referring to magnetic storage and "disc" for optical storage. wikipedia article
This patch just changes the identifier for the small version to ICON_DISC and large one to SPECIAL_IMG_DRIVE_DISC. Neither is used anywhere yet.