An option which can be exercised at any time between the purchase date and the expiration date. Most options in the U.S. are of this type. This is the opposite of a European-style option, which can only be exercised on the date of expiration. Since an American option provides an investor with a greater degree of flexibility than a European style option, the premium for an American style option is at least equal to or higher than the premium for a European-style option which otherwise has all the same features. also called American-style option.