A short film is any film not long enough to be considered a feature film, whereas feature length films are usually 90-120 minutes long, short films should have a running time of 40 minutes or less. Short films can be both amateur and professional productions, and are majority of the time screened at film festivals whether it is local, national or international. Unlike feature length films, they aren’t made with profit in mind but instead made by independent filmmakers in order to be noticed or possibly gain funding for future productions by entertainment studios etc. Short films are made on very low budgets or sometimes no budget, yet some are funded by film grants.  Companies such as the UK Film Council offer these sorts of initiatives and grants. Short films are experimental and alternative, which means the target audience, will be as mainstream as feature length. The casts are particularly small in short films due to the low budget and dependent on the size of the short film, will depend on whether they get paid or not. Similarly to the small casts, the numbers of locations are usually limited. 

Ref - 'What is short film?' Symon Quy 2007