The 180-degree rule dictates that cameras must be kept on one side of an imaginary line during filming, unless the camera is shown crossing to the other side, to maintain continuity. It is important for filming conversations so that the footage flows properly when edited together. Breaking the 180-degree rule can disrupt the narrative flow and make a scene appear inconsistent.

1. What is the 180-degree rule?
The rule basically means to keep the cameras at one side the invisible 180
degree line, unless you show the cameras moving to the other side.
Why is it important?
The 180-degree rule needs to be applied when filming conversations or
else it will not flow and look right.
This link is to a YouTube video which gives a very good
explanation of the 180-degree rule.
http://www.youtube.com/watch?gl=GB&hl=en-GB&v=HdyyuqmCW14

2. When edited, s-r-s shows cutting back and forth
between footage which has been shot at the
same time between two different cameras.
The 180-degree rule has to be applied.
Commonly used for filming conversations.

3. This editing technique is used for
continuity sequences as it makes sure
everything flows and stays the same even
though they could be separate clips.
An example of this would be making sure a
character is dressed and looks exactly the
same as they did in the previous clip, this
ensures the scene flows.

4. This is when there is a cut-away to a different location or object to show the audience
a visual clue to the narrative.