Final answer:
The DL-51 is a medical certificate required for commercial drivers to verify physical fitness to operate a commercial vehicle.
Step-by-step explanation:
The DL-51 form is known as the Medical Examination Report for Commercial Driver Fitness Determination. It is a required medical certificate that commercial drivers must carry to confirm they are physically qualified to operate a commercial vehicle. This form is filled out by a licensed medical examiner after a thorough examination. To maintain the validity of their commercial driving privileges, drivers must ensure this form is updated and submitted as required by their state's Department of Motor Vehicles or equivalent authority.