The word impression is one of the key terms in online marketing. By definition, an impression is the act of showing an advertisement to a customer. The main question that interests marketing newbies is what counts as an impression. Well, it includes literally every case of serving an ad to a customer, including the case when an advertisement is shown for the same users a multiple number of times. Impression is one of the basics of online marketing, but its significance is disputed. This is because the number of impressions is not equal to the number of clicks. Whether a user will actually be interested in the ad after an impression is made depends on a number of other factors.