What is an Impression?

An impression is one display of an ad creative to a user (or device) in an ad server or account. Base unit in CPM models, programmatic RTB, and reach reporting.

When it counts

Platform rules differ: served impression (creative delivered) vs viewable impression (50%+ pixels visible 1+ sec, MRC). Video uses quartile or completed views separately.

Funnel link

Impression → click → visit → conversion. CTR = clicks/impressions. Without a click, an impression does not send tracker traffic but affects CPM cost and view-through attribution.

Notes

Duplicates, pre-fetch, background tabs, and fraud inflate counts. Frequency caps limit impressions per user. In push/pop, click sometimes replaces impression as the billable event.