Glossary of Mobile Advertising Terms
Impression (might also be called a view or an ad view) is a term (metric) used to refer to the point when an ad is fetched from its source and displayed to the user.
Each time an ad is fetched, it’s counted as one impression and the ad doesn’t have to be clicked (just displayed) to count as one impression. The fact that the ad doesn’t have to be clicked sparks some debate on how accurate this metric is. Impressions are a common term in online advertising where income is often generated per impression basis.
Impressions are often measured by CPM (Cost Per Mile - see the definition for CPM for more information).
There are some problems when measuring impressions as there is always a possibility of a click fraud. Because of this, robotic activity is filtered and excluded, although this might not always be the case as a lot of traffic comes from bots so some might be overlooked.
Also, ads might fail to load or an incorrect one might be displayed. Since there are different types of ads there are also some variations when the impression occurs. For example, for banner ads, impression occurs when the ad is fetched and the user sees the ad, while for the video ads, impression occurs once the first frame of the video is displayed.