It is the force that the governor applies to the sleeve as it moves. The force exerted on the sleeve is 0 when the governor’s speed is constant because the sleeve does not tend to move, and thus the governor’s effort is zero. However, when the governor’s speed changes and the sleeve tends to move to a new equilibrium position, force is exerted on the sleeve. As the sleeves move to a new equilibrium position matching the new speed, this force eventually declines to zero. The governor’s effort is defined as the average force applied on the sleeve for a particular change of speed.