Explain what is the meaning of CTR?

Click-through rate (CTR) is a measure of the percentage of clicks advertisers receive out of whole ad impressions. "Impressions" refers to the number of times your ad is viewed.
A click through rate calculation looks like this: Click Through Rate = (Total Clicks on Ad) / (Total Impressions)

Click-through rate (CTR) is an incredibly important concept in search engine marketing. The simplest definition is that click-through rate is the percentage of people who click on your ad after seeing your ad.

Click-through rate (CTR) refers to the number of times a user clicks on a Web page advertisement compared to the total numbers of visitors viewing the ad.

In Internet marketing, CTR stands for click-through rate: a metric that measures the number of clicks advertisers receive on their ads per number of impressions. Achieving a high click-through rate is essential to your PPC success, because it directly affects both your Quality Score and how much you pay every time someone clicks your search ad.