Impressions refer to the number of times an ad is viewed by a user or displayed on a web page through Google AdWords or other forms of PPC advertising or the number of times a web page is listed on SERP (search engine results page). Often times Impressions are called an ad view or simply a view.
Impression is a term that refers to the point in which an ad is viewed by a visitor for the first time, or displayed once on a web page. The number of impressions of a particular advertisement is determined by the number of times the particular page is located and loaded. If it is randomly generated, then it is the number of times the particular ad appears from the random generator. An impression is an estimate of the number of people a particular advertisement is reaching, and may be counted in different ways depending upon the way the ad is situated on the page, as well as the number of times the web page where the ad appears is shown. Ad reports list the number of total times of impression of the ad, which basically counts the number of times that the ad was served by the search engine when the keywords that the ad is connected to were searched for.
Ad impressions are generally logged by a server that supports the original ads, and saves the numbers for ad reports later on. Depending on the way the advertisement is situated on a page, the advertisement might have one impression, or two. An advertisement that is listed vertically on the page, causing the visitor to have to scroll down, will be likely to list two impressions per visitor for that particular advertisement. The point of tracking the number of impressions that an advertisement has is to judge whether the advertising campaign is working or not. A campaign that is working will not only have a large number of impressions but a good conversion rate as well. A campaign with poor results may not have as many impressions as the advertiser had expected to get, and can mean that the campaign will eventually be reevaluated and changed.
While there are many different discrepancies that can be argued when counting impressions, there are as many experts who agree that there is no certain way to count impressions, as the results can be skewed not only by multiple page views by one visitor but countless other variations. As there are many different publishers in the World Wide Web, there are also many different ways to count impressions. This has led to problems between advertisers and publishers in the past. Currently, it is generally it is between the publisher and the advertiser to decide how the numbers are counted and collected. In the end, the number of impressions that an ad has is generally taken with a grain of salt by advertisers and the entire campaign is not changed because of the impression numbers alone.
Web page and ad impressions are important to search engine marketing though, no matter how varied they are. The reason impressions are counted for most advertisers is because it is an economical way to discover whether the advertisements are being looked at or not. In the end, advertisers will use other forms of reporting to decide if an entire campaign is working or not.