CDRWin (and others) Description File for a CD-Image
CUE is a file extension for a Cue sheet description file for a disk image format. The format was originally used in CDRWIN CD recording program. The file describes the way tracks are laid out on a disc and their length.
CUE files may also be used to specify album, song and artist names. CUE files are written in plain ASCII and are recognized by most burning programs.
Learn more about CUE files:
Wikipedia has an entry about CUE files.
Search for answers to CUE-related questions at IT Knowledge Exchange.