I think that you've got the emphasis in the wrong place.
It's negative feedback, of torque.
The basic principle is straightforward. There will be a device (doesn't really matter how it's done) that measures torque. This is then subtracted (negative!) from the reference torque that you should have.
The difference is "negative feedback". This is then added to the control input into the machine (prop / engine / whatever). This can be mechanical or digital, and simplistically looks like this...
The basic system, known as a negative feedback loop is the fundamental building block for controlling virtually any stable system - whether it's an engine running sped, you trying to stand upright, your heart rate....
G