in control from a reference to a controller that controls a system and tries to bring the output equal to the reference.
In your case you have for example a speed reference, a controller that is electronics, and the system is your brushless motor.
if the reference is constant we talk about "regulation", if it is variable we talk about " pursuit" (or better, of servicing).
the motor will not equal the reference, their difference is the tracking error, which depends on the type of control and the type of reference.
I studied three years at university... I don't know if I can explain myself in a few lines...
