What is a short film?

The Textbook Definition

A short film is essentially any film that is not considered long enough to be a full feature. The Academy of Motion Picture Arts and Sciences defines a short film, eligible for nomination at the Oscars, as "an original motion picture that has a running time of 40 minutes or less, including all credits." 

My Definition

Short films, according to me, are generally low-budget, independent films that hold a clear three-act structure. They are usually more dramatic, due to the small time frame although straight to the point rather than building up tension. Many short films I have watched have essentially been the start of what could be made into a major feature film, or a trailer of sorts. Just because they are shorter does not mean they lack depth, however a couple I have watched have had an incredibly unsatisfying ending. By this, I mean that the end of the short film was anti-climactic (which leaves the audience wanting more) in the sense that the narrative will spell out and just as you become more intrigued, it cuts out.