Répétiteur (Fr.), repetitore (It.), or Korrepetitor / Repetitor (Ger.), originally from the French verb répéter meaning "to repeat, to go over, to learn, to rehearse".
In opera, répétiteur is the name given to the person responsible for coaching singers and playing the piano for music and production rehearsals. Repetiteurs are extremely skilled musicians, with extraordinary powers of sight-reading and score reading. They are able to instantly arrange a large open score and follow a conductor.
In ballet, a répétiteur teaches the steps and interpretation of the roles to some or all of the company performing the dance.