An exercise interval for an American-style option that opens at the end of the option’s life (time to maturity), allowing exercise at any time within that interval (the exercise window). The option exercisable according to an American window is a type of modified American option in which the holder (buyer) can exercise in a manner similar to both American-style and European-style.

For example, a 1-month American option may come with an American window marking the last few days in its life (e.g., 3 days) during which the holder can exercise.