Click-through rate is clicks divided by impressions (or by reach), expressed as a percentage. If a post is shown 10,000 times and gets 200 clicks, its CTR is 2%. It is one of the clearest signals of whether your creative and offer are compelling enough to move someone off the feed and toward your site, product or landing page.
CTR matters because it sits directly on the path to conversion and revenue, and because in paid media a higher CTR usually lowers your cost per click and per acquisition. A high engagement rate with a low CTR often means content that entertains but does not persuade people to act.
Improve it with a sharp headline or hook, a clear and specific call to action, a link that matches the promise, and creative that pre-qualifies the click so the people who tap are the ones you want. Test variants and compare CTR by format and placement.