Click-through rate (CTR) is one of the most important factors in affiliate marketing. Its a measurement of the success of an advertising campaign. By definition, CTR is the number of visitors who click on an ad in comparison to the total number of websites visitors. It is calculated by dividing the number of clicks by the number of ad impressions. For example, if the ad was shown to the users a thousand times, which resulted in 5 clicks, the CTR is 0.5%. Apart from providing an insight about a success of a marketing campaign on a certain website, it is also used for email marketing as well.