A serial film, film serial, movie serial, or chapter play, is a motion picture form popular during the first half of the 20th century, consisting of a series of short subjects exhibited in consecutive order at one theater, generally advancing weekly, until the series is completed. Usually, each serial involves a single set of characters, protagonistic and antagonistic, involved in a single story. The film is edited into chapters, after the fashion of serial fiction, and the episodes should not be shown out of order, as individual chapters, or as part of a random collection of short subjects.