From The Art and Popular Culture Encyclopedia
Mockumentary, a portmanteau of mock and documentary, is a film and TV genre, or a single work of the genre. The mockumentary is presented as if it were a documentary recording real life, but is in fact fictional. It is a commonly used medium for parody and satire. They are often used to analyze current events and issues by using a fictional setting.
Mockumentaries are often presented as historical documentaries with b roll and talking heads discussing past events or as cinéma vérité pieces following people as they go through various events. Examples of this type of satire date back at least to the 1950s (a very early example was a short piece on the "Swiss Spaghetti Harvest" that appeared as an April fool's joke on the British television program Panorama in 1957), though the term "mockumentary" is thought to have first appeared in the mid-1980s when This Is Spinal Tap director Rob Reiner used it in interviews to describe that film.
The false documentary form has also been used for some dramatic productions (and precursors to this approach date back to the radio days and Orson Welles' production of H. G. Wells' novel, The War of the Worlds).