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, 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, then view-through conversions that happen within 30 days after an impression are tracked. A longer view-through conversion window will usually increase the number of view-through conversions Google Ads records.