Impressions are the number of times one of your pages appeared in a search result, whether or not anyone clicked it. Google counts one each time your listing is on a results page someone loaded, so a page far down on page four earns almost none while a page at position three earns one for every search.
An impression is not a visit. It is the chance of one. Impressions tell you how often Google is showing you; clicks tell you how often people took the offer. A report that celebrates impressions alone is reporting the size of the shop window, not what came through the door.
