Click-through rate (CTR) is the proportion of people who click an ad after it is shown to them. It is usually calculated as clicks divided by impressions, then expressed as a percentage. For example, 20 clicks from 1,000 impressions gives a CTR of 2%.
Advertisers use CTR to assess whether an ad attracts attention and prompts action. In cyber security, CTR can also help evaluate deceptive campaigns: a high rate of clicks on a phishing message may indicate that its wording or appearance is effective. CTR is not proof of impact on its own; it does not show whether people remembered a brand, made a purchase, or suffered harm. Defenders and marketers should interpret it alongside measures such as conversions, recall, and reports of suspicious content.