Reverse shot

Reverse shot

The reverse shot or shot reverse shot is a technique usually used when there is dialogue between two characters and we see a shot of each of them. These shots will mostly be mid shot to close up.
During production, filmmakers will need to stick to the 180o rule and keep the cameras to one side or it will distort the viewers image on who is where.

In this scene we can see that the cameras stand just behind the second actor's shoulder and their line of sight crosses over each other.

It doesn't have to be just between two people, it can be between a person and a view, place, object or animal. As long as the cameras stay within the 180 degree line then the scene will make sense.

When placing the cameras over the 180 degree line the actor's eyeline will seem like they are looking in the same direction.