Voice-over is speech laid over picture when the speaker is not shown on screen. It is used for commentary, supplementary information, inner narration and translation.
Where it fits
Its role is to deliver the necessary information, no more and no less, in step with the pace of the video. It is sometimes used as narration.
What to check when using it
Because the voice overlaps with music and sound effects, check not only the levels but also the density of the sound and how easy it is to follow.
The concept overlaps with narration, but voice-over is a term focused on how the voice is placed against the picture as a technique.
