Monetisation & Revenue
Ad Impressions
Also called: impressions served, ad impression
One playback can carry several ads, so this figure sits above the count of monetised playbacks. It is the denominator behind CPM, which measures advertiser spend per thousand ad impressions.
Two things hold it down. Not every playback is monetised, because some content is limited, some viewers are on Premium and some block ads, and mid-roll placement decides how many ads a single watch can serve. That makes it a poor proxy for reach and a decent way to check whether an inventory change, such as switching mid-rolls on, did what you expected.