Clicks are the number of times someone has clicked an ad on your blog. Impressions are the number of times an ad was delivered on your blog.
Google has a tendency to disable accounts that have a CTR that is too high. (I guess that is their way of making sure people aren't abusing the system) To stay safe always monitor your CTR. If your CTR is 15% or above REMOVE ADVERTISEMENTS FROM YOUR BLOG. To lower the CTR ask for views only.
Keep that in mind. It would suck to have "the man" shut down your blog just because it's doing well.
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