This OPC UA Property, of DataType BACnetDeviceObjectPropertyReference, represents the BACnet property Manipulated_Variable_Reference. The BACnetDeviceObjectProperty Reference DataType is defined in 10.5.9.
This property indicates an object and property that the output (Present_Value) of the control loop is written to. Generally this is a BACnet Analog Output object used to position a device, but it could also be another object or property. See the BACnet specification for additional examples.