A single instance of an online advertisement being displayed.*
* This definition may be an over-simplification, as there is no standard way to count impressions. All of the differences can add up to very large discrepancies, yet people make purchases based on impression every day.
So… what is the definition?
Currently, whatever a buyer and seller agree on.
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ClickZ (September 16, 2002)
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The Impression Must Be Destroyed! (Part 1)
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