Click-through rate is clicks divided by impressions. Out of everyone who was SHOWN your thumbnail, link or profile, CTR is the share who actually clicked. It measures your packaging: the title, the thumbnail, the first impression.
YouTube shows your video's thumbnail 10,000 times. 500 people click. Your CTR is 5%.
Nothing about the video itself has happened yet. CTR is decided entirely by the thumbnail and title, which makes it the most controllable metric you have: you can change the packaging in five minutes and watch the number move.
Here's the counterintuitive part. As a video spreads to strangers, CTR usually FALLS, because strangers click less than your fans do.
So a dropping CTR on a video that's gaining views often means the video is winning, not losing: it's being shown to a wider, colder audience. Judge CTR together with impressions, never alone.
You can spike CTR with a misleading thumbnail. The click comes, the viewer feels tricked, they leave in ten seconds, and your audience retention collapses.
Platforms weigh the pair together for exactly this reason. The packaging gets the click, the content keeps it, and ranking needs both. Honest-but-exciting packaging is the whole craft.
Most videos land somewhere in the low single digits, and it varies with audience size and where impressions come from. Compare a video against your own channel's normal, not against a universal number.
Test thumbnails and titles. Make the promise of the video clear in one glance, use readable text, and put the most curious moment on the cover. Then check the retention graph to make sure the video keeps the promise.
It can. People click what already looks watched: a video showing strong social proof wins more clicks than the same video at 63 views. That's part of why view counts get bought.
Every definition lives in the full glossary, and the services behind the vocabulary are on the services page.