A serial, film 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. Generally, each serial involves a single set of characters, protagonistic and antagonistic, involved in a single story, which has been edited into chapters after the fashion of serial fiction and the episodes cannot be shown out of order or as single or a random collection of short subjects.