a multi-part, 'short-subject' film that was usually screened a chapter/episode per week at a film theatre; the predominant style of the serial was melodrama; often, each chapter or episode, continually presented in installments over several weeks, would conclude with an unresolved cliffhanger to ensure that audience would return the following week to discover the resolution; popular until the early 1950s; contrast with series and sequels.
— Film Terms