A documentary film is a nonfictional motion picture intended to document reality, primarily for the purposes of instruction, education, or maintaining a historical record. "Documentary" has been described as a "filmmaking practice, a cinematic tradition, and mode of audience reception" that is continually evolving and is without clear boundaries. Documentary films were originally called "actuality" films and were only a minute or less in length. Over time documentaries have evolved to be longer in length and to include more categories, such as educational, observational, and even "docufiction". Documentaries are also educational and often used in schools to teach various principles. Social media platforms such as YouTube, have allowed documentary films to improve the ways films are distributed and able to educate and broaden the reach of people who receive the information.