what is an intercooler??

tach leutz!! I just found an American tuningmag (modified). great likes anyway clear, but is often written there in advertisements of intercoolers and are also pictured (bottle, hoses and so ́n ovals dings what looks like a thin tube and comes in front of the stick). so you are special now – what is/brings that and can you also drive around with it in Europe?? thank you already times and gretz