In Google AdWords, Click Through Rate (CTR) is a measure of how many people click on your ad versus how many people see your ad. CTR is an indicator of how relevant your ads are to the people who are searching for your keywords.
Click through rate is measured by dividing the number of clicks on your ad by the number impressions (or number of times your ad was displayed with search results.)
CTR = Clicks/Impressions
A higher click through rate is better–this means that your ad was relevant and attractive to potential customers. A low CTR might mean that your ad is appearing for searches unrelated to your product. This is when negative keywords come in handy. A low click through rate can also be a sign that there’s a problem with your ad copy. It might be helpful to take a look at your competitors to see how your ads stack up.