Unseen Audience

Most often, the narrator of a story is unseen, and may not even be a character within it. However, sometimes we do see the narrator, and he seems to be talking to us (the audience) breaking the Fourth Wall; but instead, he or she is actually talking to another character within the story, but we don't realize that until later. This is often done to surprise the audience with the listener's identity. It is, however, a tricky thing to do, as the author must be careful not to have the narrator mention something he couldn't know at any point, or say something that reveals too early whom he is addressing.

If this is employed by a character who is not the narrator, especially for comedic effect, then it is a Fourth Wall Psych.

Examples of Unseen Audience include:

Anime and Manga

Whoever the heck Kyon is talking to. This being that series, musing about it would create multiple Epileptic Trees.

Comic Books

In the Marvel Comics series What If?, the alien Uatu The Watcher seems to be telling the readers about the events he has observed in other alternate universes. It was later revealed, however, that he's actually recording his comments for the people who will exist after this universe is destroyed... whoever they might be.

Film

The Mockumentary Pirates of Silicon Valley starts off with what looks like a talking head of Steve Jobs. The camera then revolves around to behind Steve, revealing that he's actually talking to someone across the table from him.

Live-Action TV

Inverted in Angel. Lorne seems to be talking to a literal audience (in a theatre), but is revealed to be talking to nobody but the TV audience (though he doesn't know he's talking to us, either).
The Doctor Who episode "The End of Time, Part One" is narrated by an ominous voice eventually revealed to be Timothy Dalton as the Lord President of the Time Lords, telling the story to the assembled Time Lords (who had previously been assumed to be dead).
A few years back, an episode of ER had Luca apparently narrating his thoughts throughout. It looked pretty cheesy, and as if he was justified in turning down offers to talk to a therapist. Until the reveal, where you see that he's paid a prostitute just to sit and listen.
The Just Shoot Me episode "My Dinner With Woody", which has a Whole-Plot Reference to Annie Hall, starts with Maya talking to the camera, as Alvy does at the beginning of Annie. At the end, it is revealed that Maya had been talking to the water delivery guy.
One episode of Scrubs is narrated by Dr. Cox, speaking to an initially unknown person. Partway through the episode, Dr. Cox blames the listener for his going soft, and at the end of the episode it's revealed he's talking to his infant son.
The Twilight Zone.^[context?]

Video Games

Tends to happen with the Non-Entity General in video games.
The last case of Apollo Justice features Phoenix doing this. At first, it seems like he's addressing the player, then later, it sounds as if he's addressing Apollo and Trucy, but it is finally revealed that he has been addressing the Jurists/Lamiroir this whole time.
In Bastion, the entire game is narrated by a character name Rucks, but who he's talking to is unclear until in one of the later missions it turns out that Rucks has been recounting The Kid's journey to Zia, who wasn't there for most of it. It also gets played with, since in the very final mission, it turns out that the entire recounting took place while The Kid was off doing the final mission, and Rucks has nothing to say anymore, since they're caught up to the present, and he's got no idea what's happening or what has already happened for the final mission. The narration once Zia is totally caught up is just them talking about the future should The Kid succeed.
The interrogators in Call of Duty: Black Ops are Hudson and Weaver.
The Prince's voiceover in Prince of Persia: The Sands of Time. It is revealed near the end that he is recounting his adventures thus far to Farah.

Web Comics

The Gods of Arr-Kelaan does this twice, first with Inti the Sun God (who narrates the first part of the series to the combined Norse and Olympian pantheon) and then later with Ronson, who narrates his escape from Hell to an actually invisible goddess.
Done in Sluggy Freelance once in very random filler, in which Torg is at first clearly addressing the audience and talking about the filler (and about Breaking the Fourth Wall), but then is suddenly shown to be talking to Gwynn, who asks him why he calls her "you guys" and what the Fourth Wall is.