Apostrophe

Apostrophe is a direct address to someone absent, to the dead, to an inanimate object or to an abstract idea, spoken as though it could hear and answer.

All right then. Come on. Start. — said to a car.

The speaker turns away from whoever is actually present and addresses something that cannot reply. It is the punctuation mark's namesake and has nothing to do with it; this apostrophe is a figure of speech.

It usually pairs with personification, since addressing a thing implies that the thing could hear, and it usually takes the imperative mood, since addressing the absent almost always means asking them for something.

What it does for a reader is create the position of overhearing. A character who speaks to a dead parent, an empty flat, or a jammed printer is not performing for anyone in the scene, and the reader takes the line as unguarded in a way that ordinary dialogue is not. That makes it one of the most efficient ways to give a solitary character an interior life without narrating one.

Shakespeare uses it constantly for exactly that reason — Macbeth addressing a dagger that is not there tells the audience more than any soliloquy about daggers could.

Two cautions. It is inherently theatrical, so it must suit the register, and it rarely survives being repeated. Once per character, at the moment it costs them something.