In ancient Greek comedy, parabasis involves a direct address to the audience by the chorus. This dramatic technique allows the playwright to highlight the artificiality of the play by involving the audience as well as giving him the opportunity to heighten the overall level of humor through in-jokes and satire.
Aristophanes is a past master at the technique, as can be seen in scene 2 of The Clouds, when the chorus steps forward and criticizes the audience for not supporting the play in its earlier incarnation. The chorus further defends Aristophanes by insisting, somewhat tongue-in-cheek, upon the modesty of his humor. Unlike other playwrights, he does not stoop to vulgarity or crude sexual innuendo.
Although parabasis declined during Aristophanes's lifetime, it laid the foundations of the breaking of the fourth wall, where playwrights deliberately demolish the artificial barrier that separates the audience from the action taking place on the stage.
In the work of Brecht, for example, we see a conscious attempt on the part of the playwright to remind the audience at every turn that they're watching a play. Brecht does this, as Aristophanes does in attacking the audience in The Clouds, to drive a wedge between the audience and what's happening on stage.
In other words, Brecht demolishes the fourth wall only to erect another barrier between the audience and the drama, the better to encourage the audience to step back from the action.