This has a very broad range that it can cover. To me, a documentary is a film that depicts a person or particular person. Not a biography of a particular person, but something that tells their story or usually a struggle. It can also be an informational film on an event or new technology. For example, I found a documentary on the Bulletin Board System and the changes that have occured due to the rise of the internet.
Recently, many Americans have become aware of Documentary Director Michael Moore. He's been known for documentaries such as Farhenheit 9/11, Bowling for Columbine, Roger and Me, and Canadian Bacon. He's shed light, or at least his opinion, on events such as September 11th and the tragic school shooting in Columbine.
Roger and Me, however is not based on a particular event but the decline of a city. This documentary is based on Flint, Michigan and the decline of the economy. Through out the film, Moore attempts to interview Roger Smith, CEO of the Flint branch of General Motors. The GM plant had been a major source of income for the city, until it began to outsource jobs.
In reality, I guess a documentary can be an informational or persuasive film on almost any topic.
