A more thorough explanation:

Definition: Nonconforming use refers to when local governments change zoning laws and allow existing property some form of exemption from abiding by the new regulations.

For example, let's say a business has been operating in a certain area for many years. Suddenly, the city decides to change the zoning laws and make the area residential only. Without nonconforming use, the business would have to shut down or move to a new location. However, with nonconforming use, the business can continue to operate even though it doesn't conform to the new zoning laws.

Nonconforming use comes with limitations. The property may not expand its nonconforming use or change the property use at all unless it conforms with new zoning regulations. In some cases, the nonconforming use may only be granted for a limited amount of time, setting a deadline for the property to meet the new requirements. The owner may also be prevented from returning the property to a nonconforming use if the property starts conforming. Some kinds of nonconforming use may be outlawed by legislation.