Click-Through Rate (CTR) is a key performance metric in digital marketing that measures the effectiveness of an online advertising campaign or an email marketing campaign. It is calculated by dividing the number of clicks an ad receives by the number of times the ad is shown (impressions) and is expressed as a percentage. A higher CTR indicates that a larger percentage of people who see the ad find it relevant or compelling enough to click on. CTR is used to gauge how well keywords, ads, and free listings are performing. In the context of email marketing, it measures how many people clicked on a link within the email. CTR is critical for understanding the appeal and relevance of your content to the target audience.