Impression

Also known as: ad view

An impression is counted every time a creative (ad) is served to a user. It is one of the most fundamental campaign performance indicators in digital advertising.

Impressions are counted and reported by ad servers, which use tracking tags (pixels) for measurement. If a user refreshes a page and sees the same ad again, that counts as a new impression.

In pricing models, impressions are typically grouped into units of 1,000, denoted as CPM — cost per mille, where mille is Latin for one thousand. CPM is the standard unit rather than per-impression pricing because the cost of a single impression is very small relative to clicks or conversions — often as low as $0.002 — making it more practical to transact in bulk.