The tray of a CD-ROM drive, or by
extension the CD drive itself. So called because of a common tech
support legend about the idiot who called to complain that the cup
holder on his computer broke. A joke program was once distributed
around the net called "cupholder.exe", which when run simply
extended the CD drive tray. The humor of this was of course lost on
people whose drive had a slot or a caddy instead.