History of short film

Short film is a technical description originally coined in the North American film industry in the early period of cinema. The description is now used almost interchangeably with short subject. Either term is often abbreviated to short (as a noun, e.g., "a short").
Although the North American definition generally refers to films between 20 and 40 minutes, the definition refers to much shorter films in Europe, Latin America and Australasia. In New Zealand, for instance, the description can be used to describe any film that has duration longer than one minute and shorter than 15 minutes. The North American definition also tends to focus much more on character whereas the European and Australasian forms tend to depend much more on visual drama and plot twists. In this way, the North American form can be understood to be a derivation of the feature film form, usually acting as a platform for aspirant Hollywood directors. Elsewhere, short films tend to work as showcases for cinematographers and commercial directors

http://en.wikipedia.org/wiki/Short_film