What does M.O.S. stand for?

The term “M.O.S.” generally appears on a slate when a scene is filmed without sound.  Hollywood legend defines the term as “Mit Out Sound”.  We’ve heard many fascinating explanations of the term’s origins.

M.O.S. may have originally stood for:

• Mit Out Sound
• Mit Out Sprechen
• Minus Optical Signal
• Minus Optical Sound
• Minus Optical Stripe
• Muted on Screen
• Mute on Sound
• Mic off Stage
• Music on Side
• Motor Only Shot
• Motor Only Sync

M.O.S. A shot or scene filmed without recording sound; an event that, ironically, often seems to throw the sound department into an “Okay-but-you’ll-be-sorry” snit.

Industry mythology has M.O.S. deriving from the request of a long-gone German-speaking director— variously indentified as Erich von Stroheim, Josef von Sternberg, or Ernst Lubitsch— to film a scene “mit out sprechen” (without speaking) or “mit out sound.”

I don’t think so.  There is a less colorful but vastly more plausible origin for M.O.S.: In the early decades of sound, until the 1950s, the sound track was recorded on an optical rather than magnetic track (now always called the “mag track”).  When film was delivered to the lab for processing with a blank sound track, it was noted that it was being send Minus Optical Stripe.  Makes much more sense to me, although I understand the appeal of the apocryphal version.