Documentaries

The purpose of a documentary is to document, that is to report with evidence something that has actually happened.

It can show this by using actuality footage ('real' footage of actual events) or reconstruction. It can use a narrators voice over to anchor the meaning or rely on the participants themselves with perhaps the occasional interjection by the nature.

The term was first used by John Grierson - General Post Office Unit in 1930's.
He defined documentary as 'the creative treatment of actuality' (or reality)