What is an authorization issued by the department for the operation of a motor vehicle called?

The term that refers to an authorization issued by the department for the operation of a motor vehicle is a driver license. A driver license is a legal document that grants an individual the right to operate a motor vehicle on public roads, having met the necessary requirements set by the relevant authorities, including passing required tests for knowledge and driving skills.

A driver license serves as an official validation of both the operator's identity and their competency to drive, ensuring they understand the traffic laws and regulations. It is a crucial document that many individuals must obtain before being allowed to operate a vehicle legally.

While registration refers to the process of formally recording a vehicle with the state, and a driver permit is often a temporary authorization to drive under specific conditions, a driver license signifies full authorization and responsibility for operating a motor vehicle. Motor vehicle assignment may pertain to the allocation of a vehicle for a specific purpose or use, rather than the authorization to legally operate the vehicle itself. Hence, a driver license is the most accurate answer in this context.