Fly system in the context of Prompter (theatre)

The prompter (sometimes prompt) in a theatre is a person who prompts or cues actors when they forget their lines or neglect to move on the stage to where they are supposed to be situated. The role of the souffleur, or prompter, reaches back to the medieval theatre, but has disappeared in countries like Britain, the United States, France, and Italy. In these places, actors are expected to assist each other in case they forget their lines. However, in Germany and central Europe, the job of the prompter is still very much alive and integral to the repertory system. This is because multiple plays are performed in rotation each week, making it challenging for actors to memorise all their lines.

In theatres without prompters, their role is undertaken by the stage manager, who will have a copy of the script called the prompt book. This is the most definitive version of the script for any one performance, and will contain details of all cues, with their precise timings with respect to the action on stage. This allows the prompt to direct lighting, sound, flying effects and scene changes during a show. The prompt book also often contains blocking notes, so that the prompt is always aware of the intended positions and movements of all the actors on stage at any given time.