What is a short film?

• A short film is any film not long enough to be considered a feature film.
• The Academy of motion pictures art and sciences defines a short film as " An original motion picture that has a running time of 40 minutes or less." 
• Short films can be professional or or amateur productions.
• Short films are often screened at local, national or international film festivals.
• Short films are often made by independent film makers non profit, either with a low budget, no budget at all, and in rare cases big budgets. 
• Short films are usually funded by film grants, non profit organisations, sponsor, or out of pocket funds. 
• These films are used by indie filmmakers to prove their talent in order to gain funding for future films from private investors, entertainment companies, or film studios.
• Short films qualify for Academy Awards if screened in Los Angeles.

A short film script can be a great calling card for a writer. Writing them requires the same skills as writing a feature length script, though on a small scale. TV broadcast opportunities may be limited, but there are more outlets for these opportunity such as posting it online for example YouTube.
IndieWire: " Shorts used to be this artsy thing. But now there really is this explosion in film making, With all this new technology, short films have a lot more interest among regular people, because so many people are making them and putting them on the web. Suddenly, we're not explaining short films to people. Everybody's seen one".