CTR is the ratio of users who click on a specific link to the number of total users who view a page, email, or advertisement. Generally the higher the CTR the better. Analyzing the CTR can help you understand if your campaign is connecting in the right ways with your audience. If clicking on the link is a step to the goal you want your customers to get to, then measuring how often they are clicking on it can help you determine if that particular step is effective or not. Generally, the more targeted the campaign the higher the CTR. If you run a brand awareness campaign on the Google Display Network, then you should expect a low CTR. However, if you have a strong hook like a giveaway, or free resource, then it might increase the CTR. If you identified people on your email list and sent them a very targeted email with an offer that appeals primarily to that segment then you can expect a higher CTR than you normally get with the whole email list.