An option that expires or pays off if the underlying hits or exceeds the outstrike price. For example, in the case of an up-and-out call, the option expires at once if the underlying trades at or through the outstrike price before its expiration date. This option has a variety of versions including: up-and-out call, up-and-out put, down-and-out call, and down-and-out put. It is the opposite of an in option.

The out option is also known as a knock-out option, kick-out option, special expiration price option, out option, extinguishable option, vanishing option, etc.