a WFU is a Wildland Use Fire, and appears to be a natural "good" fire... from www.fs.fed.us
Wildfire is any fire, either natural or human caused that is burning and causing an unacceptable level of risk or threatens lives or property. These fires are actively suppressed by firefighters. 
Prescribed fire is planned and management ignited to achieve site-specific objectives under prescribed weather conditions. These fires are used to reduce fuel buildups and improve wildlife habitat among other things. 
Wildland Fire Use is a lightning caused fire managed for resource benefits as outlined in approved fire management plans.