Click Through Rate (CTR)

This term refers to the rate at which a search ad or other types of online marketing items are clicked on. It is typically expressed as a percentage e.g. the click through rate for the Google ad was 2%. This means 2% of the people who saw the ad clicked on it.
 
Takeaway
Make sure you are aware of the CTR for your ads and then invest more in ads that have a higher CTR.