Click-through rate or CTR is a way of measuring the success of an online advertising campaign. A CTR is obtained by dividing the number of users who clicked on an ad on a link, banner, or email creative by the number of impressions. For example, if a banner ad was delivered 100 times and one person clicked on it, then the resulting CTR would be 1 percent. This metric is good for PPC, search, email and banner advertising to determining the success of creative and the appropriateness of the placement.