When a character looks at the audience and comments on what is going on in the work they are in, but does not explicitly acknowledge there is an audience.
One of the mildest forms of Breaking the Fourth Wall; often seen in works where the Wall is otherwise quite solid and it would seem odd for the characters really to acknowledge it. It's not even impossible for an Aside Comment to preserve the Fourth Wall entirely intact if the character is interpreted as talking to themselves (see Thinking Out Loud) or an imaginary audience. Usually, the interpretation is left open unless there are other kinds of Breaking the Fourth Wall going on; it would be odd to say the least to comment on the matter if the Fourth Wall is solid, after all.
Sometimes used as a form of exposition where the character thinks out loud about what they're doing so that the audience will know, too; this can be done without even looking at the Fourth Wall, however. At other times, just used to deliver a punchline and/or snarky comment.
In a non-visual medium, where the characters obviously can't look at the audience, seeming to address the audience without making it explicit may suffice for this. However, the speaker visibly not looking at the audience disqualifies a piece of dialogue from being an instance of the trope.
Closely related to the Aside Glance, just taking it a step further. Compare and contrast with Fourth Wall Psych, where the idea of Breaking the Fourth Wall by addressing the audience is presented and then disproved. See also Leaning on the Fourth Wall.
Similarly, after one particularly bad stock joke he says, "That's the first time I've used that joke in 20 years."
It recomes a Running Gag in At the Circus since Groucho does it numerous times. One of the best is a scene where he is trying to get something Pauline has stuffed down her shirt, and when he realized she's done so he looks at the camera in fear and says, "There has to be someway to get that money while staying out of the Hays Office!"
The Big Store: "This is a bright red dress, but Technicolor is SOOO expensive!"
Parks and Recreation was created by veterans of the American version of The Office, and includes the same "talking head" segments that both the British and American versions of that show used. However, unlike both versions of The Office, there's never any reference to a documentary being filmed and the crew filming the talking heads never impacts the action. In practice the talking heads function very much like Aside Comments.
The tv version of Lovejoy would have Lovejoy do this in a vaguely Shakespearean way, delivering either his internal snark, or a bit of trivia about the antique, as a way of showing how his thought processes worked.
The protagonist does this in both the British and American versions of House of Cards.
Malcolm in Malcolm in the Middle does this several times an episode, in order to comment on the goings-on around him or explain the background of certain events to the audience.
Doctor Who. Corrupt Corporate Executive Morgus does this in "The Caves of Androzani". This happened due to the actor misunderstanding the stage directions, but was kept because it gives the character an air of Shakespearean villainy.
This trope was very popular in Elizabethan theater, most notably in the works of William Shakespeare, who used it over and over again. Often it's even written in the stage directions.
Eugene O'Neill's Strange Interlude is famous for its frequent use of often lengthy asides. It inspired numerous parodies, of which Groucho Marx's in Animal Crackers is merely the most famous.
Parodied in Molière's play The Miser; the eponymous character's servant makes several aside comments to the audience, complaining about the guy's greed, but the miser hears this and asks him who he is talking to.
Happens in The Phantom of the Opera during "Poor Fool He Makes Me Laugh". The husband explains to the wife that he is going on a trip and leaving her with the maid, and as an aside "Though I would happily take the maid with me".
When Torg is being very slow on the uptake: "He'll figure it out any moment now folks!" (Unless you count "folks" as a direct acknowledgement of the fourth wall. It seems to refer to the audience, but it's left vague.)
In the episode "Bridle Gossip", Spike seems to be looking at the audience directly when commenting he can't come up with a pun from Twilight Sparkle's name.
In "Sonic Rainboom", both Rainbow Dash and Rarity say out loud to no-one in particular what they're going to do next at some point, but only on one occasion each do they look at the audience while doing so, demonstrating the vague relationship such comments can have to Breaking the Fourth Wall.
In "A Bird in the Hoof", Fluttershy gives an uncharacteristically cunning look to the audience and says "Always works!" during a Road RunnerShout-Out scene where she tries to feed a bird a pill by hiding it under some seeds.
In "Magic Duel", Trixie uses her magic to remove Pinkie Pie's mouth after she insults her by summoning a computer mouse and trashcan. At the end of the same episode, Pinkie goes past the screen fade-out demanding her mouth back, to which Twilight reopens the screen to give it back to her.
In "Keep Calm and Flutter On", after Discord brainwashes a colony of beavers behind everypony's backs, he turns to the camera and whispers, "Oopsie!" Immediately afterwards, when he announces he's moving in with Fluttershy, she looks towards the audience and mutters, "Oh dear."
1973/74 episode "Dr. Pelagian's War". Dr. Pelagian has captured Wendy and Marvin and is planning his next move.
Wendy: Marvin, we've got to reach the Super Friends!
Marvin: Sure. Any idea how?
Wendy: Uh uh. [Looks at the camera and the audience] Do you?
1973/74 episode "The Mysterious Moles". Superman is examining the cooling unit on the roof of the power plant. While talking to himself, Superman faces the camera and says "It's my hunch the thieves will try to lift this with a powerful crane copter."