Reference / Glossary / Measurement
Impression
One instance of an ad being served. Under the MRC definition, an impression is counted when the ad begins to render on the user's device, which replaced the older served-impression count taken at the ad server. Impressions are the denominator of CTR, Viewability, and Frequency, and the unit priced by CPM.
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Cite this entry:
Agency Echelon. "Impression." Agency Echelon Reference, reviewed September 2026. https://agencyechelon.com/reference/glossary/impression/