Okay, kiddo, let me explain what dead mileage means.
Have you ever played with toy cars and made them drive around the house without stopping? Well, imagine if you were driving a real car and you had to drive it from one place to another, but you didn't have any passengers or any deliveries to make during that drive. That's what dead mileage is - it's when a car, truck or any vehicle has to be driven from one place to another without any passengers or cargo.
For example, let's say a taxi driver dropped off a passenger at the airport and now has to drive back to the city without any passengers. That's dead mileage - the driver is driving empty without making any money. Or maybe a delivery truck dropped off a load of packages at a warehouse and now has to drive to the next stop, which is far away and has no packages to pick up. That's also dead mileage - the truck is driving without any deliveries to make.
Dead mileage is not good for the owner of the vehicle because they have to pay for the fuel, maintenance, and wear and tear on the vehicle without making any money.
So, that's dead mileage in a nutshell. It's when a vehicle has to be driven without any passengers, cargo, or deliveries.