A Cue sheet is a unit that outputs Cue (a group of authored waveforms) as a data file to be incorporated into an application.
For example, you can create a Cue sheet for a unit such as "the group of waveforms used in stage 1 of the game," and then create the necessary Cue within that. Cue sheets are created in the "Cue Sheet Folder" in the Work Unit Tree.

See also: How to Separate the CueSheets