A window barrier option for which the barrier strike is active for more than one period during the option’s life. This means the barrier commences at a particular date after initiation and terminates some time later, then recommences at another date thereafter and terminates again some time later, and so on, till it terminates for good at a particular date before expiration.

If the underlying’s price breaches the barrier during any of the monitoring periods (the windows), then the option either knocks in or knocks out. Otherwise it will end up a vanilla option and expire at maturity.