What is an impression?
An impression is the number of times your ad is loaded on a website, app, or other platform and may be seen. Most impressions are actually tracked by load and not exactly by being seen. A Viewable Impression is one that is seen, not in its entirety, but in its majority. Impressions are not a solid count of the number of people that may have seen it, as it does not take into account frequency (one person may receive 50 impressions, but only come in the viewable range of 80% of those).