fly on the wall

Fly-on-the-wall is a style of documentary-making used in filmmaking and television production. The name derived from the idea that events are seen candidly, as a fly on a wall might see them. In the purest form of fly-on-the-wall documentary-making, the camera crew works as unobtrusively as possible; however, it is also common for participants to be interviewed, often by an off-camera voice.