Cues are marker points on the timeline which allows you to break a Composition to smaller parts by pausing the playback of the Composition whenever a new Cue has been reached - even when the Composition synced to an external source. There are 2 type of Cues - Stop and Marker, and both of them can be set to looping if needed.
The interface for managing Cues - the Cue Track is between the Timeline view and the Tracks. Every Composition has its own Cue Track.