"Charge-air cooler" is simply an all-encompassing term referring to a system that cools the compressed charge air before it is routed into the engine. Usually a charge-air cooler means an air-to-air cooler where the heat is rejected using ambient air flowing through the heat exchanger, much like the engine's coolant radiator. While the multi-stage turbocharger systems are still in use in some tractor pull classes, selected high-performance diesels, and are also being used on newer late model commercial diesels, the term intercooler and aftercooler are used synonymously today. The term intercooler is widely used to mean in-between the Turbocharger and the engine. Both terms, intercooler or aftercooler, are correct, but this is the origin of the two terms that are used interchangeably by all levels of experts.