Drip coffee - probably most popular, medium roasted, usually brewed with a "drip coffee maker". Is this what you mean by "Americano" coffee Polonus? BTW, a cup of drip coffee hes 2 times more caffeine then a shot of espresso.
When I think of american coffee I normally think of this drip (or filter) coffee. However a lot of places in Europe don't have a filter coffee machine and so the Americano was born. It is, as has been said, a watered down espresso. I have always been taught that, for best effect, you should put the hot water in the cup first, followed by the espresso...not sure why, but it does seem to taste more filter coffee like.