JOG - a small change in rotational position. A "jog" command is essentially an energy "pulse". A very quick ramp up and down of voltage and/or current is commanded with the idea that it will generate enough torque to overcome static friction and move the rotor some arbitrary fraction of a revolution. Since the duration and amplitude of the pulse are programmable, the resulting angle of the move is also variable. A drive train which contains large inertia components (either in the driven equipment, or in the electric motor, or both) need a bigger "kick" than a small-inertia train to achieve the same resulting motion.
Jog is when you command a variable frequency drive (VFD) to run at a fixed speed and direction for the propose of positioning a machine before you go to system run. Typically jog is activated by a momentary push button. When activated in variable frequency drive (VFD) this function over rides system stop and auto run inputs. It is typically a push-button kind of signal (which may be used repeatedly) to achieve the desired positioning of the rotor relative to some fixed observation point.
Jog is often DISABLED if the lubrication system for the drive train bearings (motor and/or driven equipment) is not suitable for very low speed (i.e. below 50 rpm) continuous operation.