A shadow cast is when there is screening of a movie and people will shadow the movie in costume. Most known for the Rocky Horror Picture Show having thousands of shadow casts in America. All of the time they will be held at night or in the morning so the theater won't loose any money showing it. Also the group performing needs to rent the movie from the company that realsed the film. Most of the time the shadow cast is of cult films.
That shadow cast of Repo The Genetic Opera was way better then that Rocky Horror Picture one.