CTR stands for Click Through Rate, and is the number of clicks an online ad receives divided by the number of times the ad, ad unit, or page is viewed. The click-through-rate is measured in how many clicks have been generated as a percentage of how many times the advertisement has been displayed.

It is a simple measure of direct response to any advertisements but as it doesn’t necessarily signify conversion, it has taken a back seat when it comes to measuring the efficiency of a campaign.