A-R-Traduction (asker) Jul 20, 2015:

I think it is a small electrical motor

A-R-Traduction (asker) Jul 20, 2015:

It deals with short sheet so I do not have a lot of context. Another sentene I found in another sheet.
Apply High Temperature Grease to the o-ring of each Winchester pin of the Motor Gearbox Assembly.
Perform the Bay Lite test 1 of the Motor Gearbox Assembly described in “Procedure for manufacturing functional test bay lite, SLS Muzic Trigger”.

Tony M Jul 20, 2015:

@ Asker Overall context? The problem is that 'gearbox' in EN is ambiguous: it may mean a box that enables you to change gear ratios (as in a car) OR a box that simply (normally) reduces the rotational speed of a motor to the slower speed usually required by most driven items.

So we need enough of your context to know what type of 'motor' this is (electric, or other?) and whether this is a fixed-ratio gearbox or a speed-changing one? And whether it does indeed reduce the motor speed (the normal case) or increase it (less common).
Unless they have a VFD, most electric motors tend to run at a limited number of more-or-less fixed speeds, usually dictated by the powerline frequency in the country concerned (normally 50 or 60 Hz, unless for aircraft (400 Hz). Hence why many applications that require a specific end speed are likely to need some kind of a gearbox in order to produce the right speed to drive the particular equipment concerned.