Page Impression and Ad Impression in internet marketing terminology refers to a single display of an ad or a page to a user. Some ad units include several individual ads within them and are counted as several impressions depending on the number of ads. In this case one page impression results in several ad impressions. Impressions can be either unique or non-unique (or repeating). Unique impression is a single display of an advertisement to a user for the first time, whereas a non-unique impression by definition refers to the second and further display of an advertisement to the same user.