Vehicle inspection is a procedure mandated by national or subnational governments in many countries, in which a vehicle is inspected to ensure that it conforms to regulations governing safety, emissions, or both. Inspection can be required at various times, e.g., periodically or on the transfer of title to a vehicle. If required periodically, it is often termed periodic motor vehicle inspection; typical intervals are every two years and every year.
In some jurisdictions, proof of inspection is required before a vehicle license or license plate can be issued or renewed. In others, once a vehicle passes inspection, a decal is attached to the windshield, and police can enforce the inspection law by seeing whether the vehicle displays an up-to-date decal. In the case of a vehicle lacking a windshield (e.g., a trailer or motorcycle), the decal is typically attached to the vehicle body.
Source: https://en.wikipedia.org/wiki/Vehicle_inspection
