A short comment or speech that a character delivers directly to the audience, or to himself, while other actors on the stage appear not to hear is called -

Normally playwrights use characters’ dialogues to tell their stories, but often it becomes difficult for them to express what their characters are thinking. Hence, they use a typical dramatic device, called “aside,” to solve this problem.

An aside is a short comment or speech that a character delivers directly to the audience, or to himself, while other actors on the stage appear not to hear. Only the audience knows that the character has said something to them.

In essence, through an aside, a character comments on what happens in the play. Simply, we can define aside as a short commentary that reveals private opinions and reactions of the character. However, it refers to the major conflict in a play, though it may not involve his personal conflict.

Source: literarydevices.net