Breaking the fourth wall.

Traditionally when talking about "Breaking the fourth wall" people automatically think of the theatre. However it is also a term used in film. It means when an actor or actress talks directly into the camer, addressing the audience directly rather than staying in the film world.

The idea of the fourth wall was brought about by a philosopher named Dennis Diderot with the advent of theatrical realism, this extended to the idea about having an imaginary boundary between any form of fictional work and the audience or viewer. Speaking directly to the audience is or acknowledging the audience is called "Breaking the fourth wall". 

Often its comedy that uses the technique of breaking the fourth wall, it allows the actor or actress to share their joke, almost like you would a private joke to a friend. One of the most prominent examples where its done very well is in the BBC comedy Miranda. 

However of course there are instances where breaking the fourth wall has been used cleverly in seriousness. For example in Othello, Iago played by Kenneth Branner he often breaks the fourth wall and addresses the audience. This is often when times are tense, adding to the suspense. Iago is the evil character, through talking directly to the audience, he is revealing his inner most feelings, which provides some dramatic irony for the audience.