A short film has many definitions, this is because it is a complex genre of film. My personal definition of a short film is a film that has a relatively low running time, normally less than ten minutes, as well as having a deep underlying and often controversial message.
Raindance.org say that a short film has seven main rules: that it should be as short as possible, keeps its practicalities, is a very visual representation, is about a single moment, tells a story, engages viewers and avoids cliches. This opinion gives a clear structure on what makes a short film successful, these rules are very important as they will give it an edgy meaningful feel.
BBC-Film network believe that the main definition of a short film is a film that is short and allows directors to try out new ideas and concepts, this opinion is well supported by the nature of short films as they often have aspects that are new and would seem experimental to a new audience
Sundance.org believe that a short film is a way to artistically express the opinions of those who created it and should always last less than 49 minutes, although longer than normal timing it is easy to see how this is true as it is limited to a certain time as well as keeping the aspect already discussed by my other two sources of having an experimental, artistic feel to it.