Any movie with a runtime that is too short to be categorized as a feature film is referred to as a short film. A short film is described as “an original motion picture that has a running time of 40 minutes or less, including all credits” by the Academy of Motion Picture Arts and Sciences, From the 1920s until the 1970s, short films in the US that were limited to two or less 35mm reels were referred to as short subjects, and films with three or more reels were referred to as featurettes. It could be shortened to “short” for either term.