Impressions are used to quantify the number of digital views or interactions with a piece of content, usually an ad, digital post, or web page.
Impression counting can often fall into a gray area, such as whether it includes repeat views, interactions with bots, or whether an impression is even an effective way to measure the success of a digital marketing campaign.
From a technical standpoint, ad servers provide a subtle image (or “pixel”) that can be found on every publisher page. When the page with this pixel image is loaded, an impression occurs.