The 180-degree rule

The 180-degree rule is a basic guideline regarding the on-screen spatial relationship between a character and another character or object within a scene.
An imaginary line called the axis connects the characters, and by keeping the camera on one side of this axis for every shot in the scene, the first character is always frame right of the second character, who is then always frame left of the first.
The camera passing over the axis is called jumping the line or crossing the line.
The 180-degree rule enables the audience to visually connect with unseen movement happening around and behind the immediate subject.