Short answers, pulled from the story.
The Academy of Motion Picture Arts and Sciences defines a short film as an original motion picture with a running time of not more than 40 minutes, including all credits. Other organizations use different thresholds; the Academy of Canadian Cinema and Television allows 45 minutes for documentaries and 59 minutes for scripted narrative films.
The first films were presented in 1894 through Thomas Edison's kinetoscope, a device designed for individual viewing. All films at the beginning of cinema were very short, sometimes running only a minute or less, and it was not until the 1910s that films started to exceed about ten minutes in length.
The rise of the double feature shifted studio distribution toward packages built around two main features, which crowded out short subjects commercially. In 1938, three major short-comedy producers, including Hal Roach and the Vitaphone studio owned by Warner Bros., discontinued their short-subject production in the same year.
Tropfest claims to be the world's largest short film festival. It originated in Australia in 1993 and now takes place in Australia, Arabia, the United States, and elsewhere. Couch Fest Films, part of the Shnit Worldwide Filmfestival, separately claimed to be the world's largest single-day short film festival.
The International Short Film Festival Oberhausen in Germany, running since 1954, the Tampere Film Festival in Finland, running since 1969, and the Clermont-Ferrand International Short Film Festival in France, running since 1979, are among the oldest festivals dedicated to short films and are still considered the most important in the world.
Pixar has screened a short film before each of its feature films during initial theatrical runs since 1995 and has been producing shorts on a permanent basis since 2001. After Disney acquired Pixar in 2006, Disney also began producing animated shorts, starting with How to Hook Up Your Home Theater in 2007.