CTR (click-to-install rate, or install rate) - the number of downloads per click
CTR demonstrates how clicks on links or clicks on your banner ad are converted into actual app installs. It is calculated as the ratio of the number of successful installs to the total number of clicks. The resulting value is multiplied by 100 to see the result as a percentage.
The average CTR in the industry is between 1-4%: if you are running an advertising campaign with pay per click, keep in mind that it will take 25-100 clicks for one successful installation.
Sometimes it is more profitable to pay not for a click, but for showing (more precisely, for a thousand impressions) an ad. But in this case, you definitely need to track the Click Through Rate, that is, the ratio of the number of clicks to the total number of ad impressions.