What is a Intercooler?
There is some confusion in terminology between aftercooler, intercooler, and charge-air cooler. In the past aircraft engines would run turbochargers in stages where the first stage compressor would feed the inlet of the second stage compressor that would further compress the air before it enters the engine. Due to the extremely high pressures that would develop an air cooler was positioned between the first and second stage compressors.
That cooler was the "Intercooler". Another cooler would be positioned after the second stage, which was the final compressor stage, and that was the "aftercooler". An aftercooler was the cooler whose outlet fed the engine.
A charge-air cooler is simply an all encompassing term meaning that it cools the turbo's air charge 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 intercool and aftercooler are used synonymously today. The term intercooler is 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.