I was listening to a webinar today when the presenter mentioned the term Burned Counties several times. I wish she would have clarified this. I presumed that it was a term from the US but I asked Google for further clarification.
The Family Search Wiki provided me with an answer.
The phrase “burned counties” was first used for research in Virginia where many county records were destroyed in courthouse fires, or during the Civil War. The strategies for researching places where a local courthouse or repository was wiped out by fire, tornado, war, flood, hurricane, earthquake, insects, rodents, mold, neglect, foxing, theft, tsunami, or cleaning-streak clerks are useful in similar situations all around the United States, Canada, and throughout the world.