O.S. is a directional abbreviation for "off screen" in screenwriting and simply means that a character may be speaking in the scene being shot but is not captured on camera.

Usage

O.S. is used as a way of focusing in on the reactions one particular character or characters to an unseen character.

Format

O.S. is specifically placed in parentheses to the right of the character name.

Example

Mary stands meekly against wall at the annual office Christmas party. She watches John approach. She looks away.

JOHN (O.S.)

Pilates. It must be the pilates because I'll tell you, Mary, you look awesome.

Mary gives a blushing smile as she inadvertantly runs her hands over her hips.

MARY

Is that the best you got?