The percentage of impressions that were measurable with Active View, out of the total number of impressions.
This metric only includes impressions from regular AdSense for Content and AdSense for Video ad units, it doesn't include data from link units, or data from dynamic allocation in Google Ad Manager.
Learn more about Active View data in reporting.
Note: Even when an ad has Active View, some factors may prevent the tag from capturing data. For example, if the publisher ad tag is placed within a cross-domain iframe, its viewability may not be measurable. Also, when an ad's backup image displays or a default ad serves, the impression doesn't count as measurable.