(O.S.) - off screen
When a character talks (O.S.) that means that he is on site and part of the scene but not seen on the screen while he/she speaks.
(V.O.) - voice over
When a character talks (V.O.) it means that he is not physically part of the scene. Strictly speaking he/she doesnít even have to be on site if her voice only appears as voice over in the scene.
Even if he is in the scene and hears his own voice but his lips donít move - thatís still a voice over.
Moreover, the Screenwriterís Bible says that any kind of narration is a (V.O) - no matter whether the character who talks appears physically in the scene or not.
For example, if a character explains something about pages in a book and the camera shows the pages or images while he is talking - thatís a voice over. It doesnít matter whether he closes the book later in the scene and goes on talking. Of course, the direct talk after closing the book will be neither (V.O) not (O.S), but just ordinary dialog.
MORE and CONTíD / CONTINUED
There is only one situation where you should use the MORE/CONTINUED construct. That is when a characterís dialog lines are interrupted by the end of the page and continue at the top of the following page: