Engines produce a lot of heat, and a lot of that ends up in the engine bay, which is typically the same location as the air intake system. A cold air intake system is designed to keep the hot air from entering the intake. This is usually done by sectioning off the engine from the intake passageways, though it can sometimes section off only the air filter. The air in the air intake section is usually coming from the ouside air, and this can sometimes be ram air. However, when forced induction becomes involved, it usually loses the term "cold air intake".
Is an Intercooler a Cold Air Intake?
An intercooler cools air before it enters the engine, but it does this cooling after the air has entered the intake system, so it is not a cold air intake system. It can, however, be used in addition to one.
How Cold Air Improves Performance
Cold air is more dense, which means there is more of it in a given space than there would be if it were hot. This means that more air can get into the engine per combustion cycle, and when more fuel is added, the engine can produce more horsepower. A fuel injected engine will use its computer system automatically adds more fuel to get more power from the extra air, while traditional carburetted engines need to be adjusted manually.
Does Cold Intake Air Reduce Engine Temperatures?
No, a cold air intake does not considerably drop the engine temperature, because any benefit the cold air would have on cooling the surfaces it passes by is cancelled out by the increased heat of the combustion it improves. There can be some minor benefits, but it in this same way, it could actually raise engine temperatures, depending on the design of the engine and how much it improves the combustion.