The 180-degree rule helps filmmakers keep the camera on one side of an imaginary line between two characters or objects, so the scene stays clear and the characters don’t suddenly switch places on screen.
Imagine two people are talking and standing facing each other. There is an invisible line between them.The camera should stay on one side of this line.
— Person A — Line — Person B —
If the camera moves to the other side, it looks like the people suddenly switched places, which can be confusing.