Any film not long enough to be considered a feature film for individual release at cinemas or on television.
A short film is any film not long enough to be considered a feature film for individual release at cinemas or on television.
According to the Academy of Motion Picture Arts and Sciences, American Film Institute, and British Film Institute, a feature film runs for 40 minutes or longer, while the Screen Actors Guild states that it is 80 minutes or longer.
From Short film on Wikipedia.