The Number of Ad Impressions shows the number of times your ad on a specific platform has been seen. Essentially, this number accounts for every instance that an ad appears on a user's screen–even those outside your desired audience.
An impression is counted as every time your ad appears on the relevant social media platform. A viewable impression is counted as every time at least 50% of your ad is visible onscreen for at least one second; in large display ads (at least 242,500 pixels), 30% of the ad must be visible for at least one second.
Meanwhile, a served impression is counted every time an ad is ‘served’ (sent) to a publisher by an ad server, regardless of whether the ad is viewed, downloaded, or rendered.
The Number of Ad Impressions is a relevant KPI for your marketing team to follow.