If an actor speaks directly to the audience, does something to the audience, or even simply notices the audience, it is known as “breaking the fourth wall”. In a movie, or on television, this can be done by the actor speaking directly to the camera.
What is it called when the actor is talking to the audience?
An aside is a dramatic device in which a character speaks to the audience. By convention, the audience is to realize that the character’s speech is unheard by the other characters on stage. It may be addressed to the audience expressly (in character or out) or represent an unspoken thought.

If an actor speaks directly to the audience it is called an aside.

If an actor speaks to himself, while only the audience can hear, it is called soliloquy.

The fourth wall is a hypothetical barrier between the actors and the audience. This barrier is broken when an actor interacts with the audience through an aside.

a member of a group of people who support the enemies of the country they live in and secretly help them: He was ambivalent about his role as a fifth-columnist.

What is the 1st 2nd 3rd and 4th estate?
France under the Ancien Régime (before the French Revolution) divided society into three estates: the First Estate (clergy); the Second Estate (nobility); and the Third Estate (commoners). The king was considered part of no estate.

Why do they call it the Fourth Estate?
The “fourth estate” is used to emphasize the independence of the press, while the “fourth branch” suggests that the press is not independent of the government.