Ad View is an impression that is accrued after the first frame of an ad is displayed.
Display ads are considered viewable when at least 50% of the ad is visible for at least 1 second. For large display ads of 242,500 pixels or more, the ad is considered viewable when at least 30% of the ad is visible for at least 1 second.
Video ads are considered viewable when at least 50% of the ad is visible while the video is playing for at least 2 consecutive seconds.