In most films everything is done as a voice over. the actors say their lines on set but then in the dubbing procees the com into a studio and read their lines again whilst watching the action. It's all very painstaking but whist filming, you can't get the mics close enough to get a good quality sound. It's then up to an editor to sync up the re-enacted voice parts to the picture. Anyway a voice over is called just that, and a sound effect id called likewise. Written down they are v/o and fx