In entertainment, we as fans act as an audience to be entertained. While being entertained, we are in a role that acts as a complete bystander. By that, I mean that there’s no actual direct communication with the entertainment and yourself. Vin Diesel’s not saying your full name with a “thank you for watching” tagline at the end of Fast & Furious. This barrier between the actor and you is called the fourth wall (4th wall).
There are in fact some forms of entertainment that break the 4th wall. An example of this is the circus. You watch as the acrobats swing from the ropes and clowns do magic to entertain. Although, at a certain point of the show there’s a time in which the Circus picks people from the crowd to interact with the show. This is called breaking the 4th wall because the show is in direct communication with the audience.
There are some movies such as Austin Powers in which Austin frequently has dialogue with the camera as if he’s talking directly to you. Many video games have scenes in which the characters talk directly to the person behind the screen. In some unorthodox stage plays they will use the audience as props for their show. In TV shows and cartoons the creators will leave subtle 4th wall breaks within the script.
Breaking the 4th wall is usually a shocking occurrence. This is because it turns you from a bystander into a part of the entertainment. While it may be strange, it is an interesting way to grab the attention of viewers and even surprise them.