A film term for a shot taken without synchronous sound, for use in a sound film. That is, a shot which will ultimately be dubbed, foleyed, and/or masked with music and ambient sounds in post-production. M.O.S. shots are shots for which live synchronous recording is not critical, and so they are shot silently in order to speed up production and avoid the unnecessary effort and expense of recording and synching the sound.

The origin of the term is uncertain, but there are two common theories.

One holds that M.O.S. stands for “Missing Optical Sound.” This refers to the fact that sound is printed optically onto film, and that it was originally recorded this way in the early days of sound film recording.

The second theory, which is more quaint and therefore more eagerly embraced by those who love early film production anecdotes, holds that M.O.S. came from a mockery of the speech of one or several German immigrant filmmakers who moved to Hollywood, such as Fritz Lang, Ernst Lubitch, or the visiting director F.W. Murnau. It is said that some witty camera assistant produced M.O.S. as an acronym for “Mitt Out Sound,” and the phrase stuck as a standard industry term.

Incidentally, besides writing “M.O.S.” on the slate, there are two standard ways to indicate that a shot is being taken without sound. One is to use a slate without a clapper. The other is to hold the clap slate with one's fingers through the space where the clapper would normally drop, to show that the clapper will not be used.