Clickthrough rate (CTR) is the number of clicks your ad receives divided by the number of times your ad is shown (impressions). Your ad and keyword each have their own CTRs, unique to your own campaign performance.

A keyword's CTR is a strong indicator of its relevance to the user and the overall success of the keyword. For example, a well targeted keyword that shows a similarly targeted ad is more likely to have a higher CTR than a general keyword with non-specific ad text. The more your keywords and ads relate to each other and to your business, the more likely a user is to click on your ad after searching on your keyword phrase.

A low CTR may point to poor keyword performance, indicating a need for ad or keyword optimization. Therefore, you can use CTR to gauge which ads and keywords aren't performing as well for you and then optimize them.

CTR is also used to determine your keyword's Quality Score. Higher CTR and Quality Score can lead to lower costs and higher ad position.