Continuity editing is the process of which shot sequences are arranged in a way that it flows and maintains a clear continuous narrative action. It is widely used in television and film, and allows a story to progress understandably. An example of fantastic continuity would be where it is virtually invisible to notice. If the continuity of a sequence wasn't clear then it would confuse the audience as to what is happening. The styles it uses to create seamless continuity work together through a variety of techniques. An example i have found on you tube shows continuity well.
In this video we see two characters acting out a scene in which they use the 180 degree rule. Subject a is on the left and subject b is on the right and this doesn't change. This is one of the techniques you can use in order to keep continuity throughout a film.