In many circumstances, monetary policy can help keep the economy on its sustainable path at full employment by adjusting the policy rate to reflect movements in the shorter-run neutral rate. In this context, the appropriate reference for assessing the stance of monetary policy is the gap between the policy rate and the nominal shorter-run neutral rate.
So far, I have been focusing on the shorter-run neutral rate of interest that is responsive to headwinds or tailwinds to demand. The longer-run equilibrium rate is a related concept.