View-through conversion window – definition
The period of time after an impression during which a view-through conversion will be recorded. View-through conversions occur after an ad impression if the user doesn’t interact with the ad but then later converts.
You can set your view-through conversion window when you create or edit conversion actions. For example, if you pick 30 days for a conversion action, view-through conversions that happen within 30 days of an impression are tracked. A longer view-through conversion window will usually increase the number of view-through conversions that AdWords records.