Aside

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. An aside is usually a brief comment, rather than a speech, such as a monologue or soliloquy. Unlike a public announcement, it occurs within the context of the play. An aside is, by convention, a true statement of a character's thought; a character may be mistaken in an aside, but may not be dishonest.
Examples.
This technique is used by many playwrights, including William Shakespeare. For instance, in the play "Macbeth", Macbeth has the following aside:
Another example is found in "Hamlet":
This technique has frequently been used in film comedy, for example in the Bob Hope "Road" comedies, Woody Allen comedies and in "Ferris Bueller's Day Off". The Jean-Luc Godard film "Breathless" contains an early use of character aside.
More recently, it is used by Ian Richardson's character Francis Urquhart in the 1990 BBC mini-series "House of Cards", as well as Kevin Spacey's character Frank Underwood in the 2013 Netflix original series of the same name. It can be used to explain the often complex politics on the show, describe what the character's plans/emotions are or simply for humorous effect.
Uses.
Aside is used to gossip about other characters without their awareness, give audiences better understanding of matters, as well as make audiences laugh; this humour that may be generated is because the character or characters being talked about is or are not conscious of the fact they are being spoken of.