From The TV IV
A documentary is any production—be it film or TV—which is intended to be non-fiction. It may include informational pieces, how-to, historical or news pieces. In general, documentaries rarely employ actors, although some actors may appear in "re-enactments"—staged, scripted scenes intended to give an idea of what the original moment, not captured on film, may have looked like. Although reality shows and game shows are technically documentaries in the truest sense of the term, the very terms have been used to distinguish that type of programming from traditional documentaries, in which the events depicted were not artificially created for the purpose of having something to put in a television show.
See the Documentary category for a list of shows done in a documentary style.