The total number of impressions that either weren't served to a person or that didn't enter the viewable area of a person's screen.
How It's Used
Waste impressions tell you how many of your ads may not have provided value because they were not delivered to a person, or did not appear on-screen. You can use this metric to understand where there is waste in your spend.
How It's Calculated
Waste impressions are the sum of impressions that weren't served to a person and the number of measurable impressions that didn't enter the viewable area of the screen.
* Nguồn: Facebook