No, that’s not quite it, @ELeahy -- it can be confusing, for sure! Maybe a practical example:
Let’s say I have a list of 100 people that I send an email to. 30 people open that email. 10 of those 30 people click a link in that email.
The Click rate would be 10 clicks / 100 sends, or 10%.
The Clickthrough rate would be 10 clicks / 30 opens, or ~ 33%.
So I could say, then, that of the list I sent it to, 10% of the people clicked something. I could also say that of the people who opened my email, 33% of them clicked something.
Now, suppose you had similar results across all your email sends. An interesting way of looking at it would be to say “Well, I know that when I send an email, only 10% of my list are going to click something. But I know that of the people who open my email, more than a third will click something. So, I’m going to focus on improving my subject lines to see if I can get more people to open my emails.”
Hope this is helpful!