Sacrificial Layer

A Sacrificial Layer is any coating which is applied over paintwork which will receive wear in place of the paintwork. As an example, if you put a layer of wax on your car, the sun, the rain and the elements will wear it away and burn it off over time until it's gone. This is why you need to keep applying wax coatings regularly, because they will wear off. However, as long as you have a good coating of wax on your car, it is this that is receiving punishment from the elements and not your car's paintwork.

Technically speaking, any coating you put on your car's paintwork is a sacrificial layer, regardless of how tough and permanent it is.