A more thorough explanation:

The second-permittee doctrine is a principle in insurance that applies when a third person is allowed to use an insured's car with permission granted by someone else to whom the insured gave permission to use the car. Under this doctrine, the third person's use of the car will be considered a permissive use under the insured's automobile-liability-insurance policy, as long as that use falls within the scope of the permission originally given by the insured.

For example, suppose John owns a car and gives permission to his friend, Tom, to use it. Tom then allows his friend, Mike, to use the car. If Mike gets into an accident while driving the car, the second-permittee doctrine would apply. As long as Mike's use of the car falls within the scope of the permission originally given by John to Tom, John's insurance policy would cover any damages resulting from the accident.

The second-permittee doctrine is important because it helps ensure that individuals who are allowed to use someone else's car with permission are covered by the owner's insurance policy. This can provide peace of mind for both the car owner and the individuals who are given permission to use the car.