accessory apartment

A separate living unit created within a single-family home and occupied by either a family member or a non-family tenant. Generally, such units are outlawed by local Zoning and Housing Codes although some cities conduct special programs to encourage such units for specific purposes.
Example: Mrs. Andrews was left with a large home when her husband died. Through a special program conducted by the city, she was able to create an accessory apartment in her home and rent it to another widow. This provided low-cost housing for the tenant and additional income and companionship to Mrs. Andrews.