Wrap was a phrase used by the director in the early days of the film industry to signal the end of filming. Since the 1920s, filmmakers have been using this phrase when principal photography is concluded and the film is ready to go into post-production. At that point, it is traditional to hold a wrap party for the cast and crew of the film. This marks the end of the actors' collaboration on the film. They may be called in to promote the film when it is about to be released.
The term "wrap" is sometimes said to be an acronym for "Wind, Reel and Print", although this is disputed, and most likely a backronym.