explanation :
This term refers to movies and TV shows in which an actor who doesn't appear narrates or describes a scene.  This technique is used all the time in documentaries, and also in dramatic films. 

e.g. In the movie "Spiderman ",actor Tobey Maguire as Spiderman performs a voice-over at the beginning and end of the film.  "Titanic" is another example of a popular film that uses voice-over.