A Truman's Wall is a specific type of Fourth wall (imaginary boundary between viewer and performer) that is also a Platonic Cave (where the entity inside is ignorant of a larger reality).
The naming trope is The Truman Show, a film where the main character is unaware his entire life is artificial-- and being observed each moment by the entire world. When he attempts to flee his island home by sail boat, he crashes into a wall at the horizon. Only then does he begin to realize that he is inside of an artificial world, thus breaking out of the Platonic Cave.
Though he once was unaware, Truman becomes aware of his audience. He then proceeds to also break the fourth wall by turning around and waving at the camera and repeating his catch phrase to the wide-eyed live television audience.
Interestingly, a Truman's Wall must also be an Inner, or nested, Fourth Wall. A fourth wall exists between Truman and his FICTIONAL in-movie audience and also between the FICTIONAL audience and the TRUE audience (the viewers).
In this case, the well-known fourth wall still remains unbroken. Neither Truman nor the ficional audience ever communicates with us at home. But something has been broken--something like a fictional fourth wall. Truman's Wall.
- Stranger than Fiction Harold can't figure out why he seems to hear someone narrating everything he does. He comes to discover that he is a character in a novel-in-progress, and begs his creator to write a happy ending.