What is a nonconforming use in zoning law?

A nonconforming use is a property use that was legally established before a zoning change but no longer complies with the new zoning requirements. Also called a grandfathered use, it is allowed to continue under the legal principle that retroactively eliminating lawful uses would be unfair. However, nonconforming uses typically cannot be expanded, intensified, or rebuilt if substantially destroyed. If the nonconforming use is abandoned for a period specified by local law, the right to continue it is lost permanently.