Stands for "Click-Through Rate". This is how many people who see your thumbnail/title, click on the video. If 100 people see your thumbnail/title on youtube, and 4 click, your CTR is 4.00

This is probably the most misunderstood stat across YouTube.

Even Youtube employees have said that it's not as useful/intelligent as they had hoped.

In reality, this number changes a lot... day to day, hour to hour, depending on where people watched the video from, etc.

When A/B testing, do not put all your eggs in this basket.

You can have a high CTR, but low views, and vice versa.

Unfortunately, succeeding on YouTube is not as simple as making one number go up.

But hopefully with better understanding and data, you can make better decisions.

CTR is not exactly #views/#impressions - some views don't count towards CTR.

For example, External views (views from twitter/etc) don't count towards CTR.

CTR also differs between view sources - you can have a high Browse CTR, but a low Suggested CTR.

CTR is useful in very particular scenarios, for example if a video had very low CTR, and very high AVD/impressions, you might consider changing the thumbnail/title, as it's possible that the packaging (thumbnail/title) is not strong enough to get people to click.

But, even this requires some nuance - if you have a high CTR, but low views, it's possible that the thumbnail/title is good, but the video itself is not good enough to keep people watching.

The big takeaway from this is that CTR is not the end-all-be-all stat. In fact, often times it's a distraction. It can be useful, but only the full picture can tell you what's really going on.

When you start going viral, CTR will start to drop, as YouTube is now recommending the video to broader and broader audiences.

This is to be expected, and is one of the reasons why CTR is not a great stat to focus on.