A motivated edit or motivated cut as it is also known, is when the scene cuts to another scene or object that was not in the previous frame. This is done in a discreet manner so as not to come off as jarring to the audience or break the illusion of continuity. Motivated edits are usually justified by narrative means such as in Flashbacks, to create a sense of tension and reverse shots.
You see it all the time in horror films: a woman is standing in a spooky place all alone and then hears a startling sound. She spins her head around and sees nothing. The sound then comes from another area, and the soon-to-be victim jerks her head in that direction. Eventually, the viewing audience gets to see the object of terror, usually along with a loud, startling sound. The scene in which the second person is killed in the recent vampire film, 30 Days of Night (2007), is a perfect example.
This is a film technique in which one character is shown talking to another character (usually not in the same shot) and then the other character is shown looking back at the first character. Since the characters are shown facing opposite directions the audience will believe the assumption that they are facing one another.
Here is an example: http://www.youtube.com/watch?v=7oTNNjRuqbE
Great scene from a great movie.