The 180 Degree Rule

The 180 degree rule is when is when you film a scene using two different shots. The camera doesn't move more than 180 degree around the characters. This allows the audience to understand where everything in the shot is. 

For example if you were to  shoot a conversation between two people looking directly at each other the line which the axis of action is an infinite line that connects their two faces. 

 

 An example of a 180 degree is shown in the shot below, this is from Harry Potter and the Deathly Hallows Part 1. This is between Harry and a man who wrote an article for the daily prophet. This shot allows the audience to see what is happening between both characters at that point. The 180 degree shot allows us to see that they are having a serious conversation, we can understand this as they have direct eye contact with each other. This shot also allows the audience audience to see its a serious converstaion through the characters facial expressions.