Click-Through Rate (CTR) is a metric used to measure the effectiveness of online advertising and content. It represents the percentage of users who click on a specific link compared to the total number of users who view the content. For example, if 100 people see an ad and 5 click on it, the CTR would be 5%. A higher CTR indicates that the content is engaging and relevant to the audience, while a lower CTR may suggest that improvements are needed. Marketers often analyze CTR to optimize their campaigns and enhance user engagement with their websites or ads.