A cast recording is a recording of a stage musical that is intended to document the songs as they were performed in the show and experienced by the audience. An original cast recording or OCR, as the name implies, features the voices of the show's original cast. A cast recording featuring the first cast to perform a musical in a particular venue is known, for example, as an "original Broadway cast recording" or an "original London cast recording".
Cast recordings are (usually) studio recordings rather than live recordings. The recorded song lyrics and orchestrations are nonetheless identical (or very similar to) those of the songs as performed in the theatre. Like any studio performance, the recording is of course an idealized rendering, more glossily perfect than any live performance could be, and without audible audience reaction. Nevertheless, the listener who has attended the live show expects it to be an accurate souvenir of the experience.
