Impressions track how many times a webpage or element on a webpage is viewed. It is one of the standard metrics used in website analytics software. The term "impressions" most often refers to page impressions, which is synonymous with page views. Each time a page is viewed, a page impression is counted. Therefore, a single visitor can rack up multiple impressions on a website by visiting multiple pages.
Unique impressions, or page views by different visitors, are useful for measuring the number of daily unique visitors to a website. Website analytics software may record unique impressions by either saving a 24 hour cookie on visitors' browsers or by resetting the record of unique visitors at the start of each day. Most analytics software records both total and unique impressions. These two metrics can be used to determine the average number of pages visitors view before leaving the website.
While impressions typically refer to page views, they may also define how many times individual elements on a webpage are viewed. For example, in online advertising, "ad impressions" track the number of times individual advertisements are displayed. If a webpage contains three ad units, each page view will produce three ad impressions. By tracking the number of ad impressions, webmasters can monitor the performance of individual ads. This information can be used in combination with RPM, or revenue per 1,000 page views, to determine the ideal amount of ads for each webpage.