The click-through-rate (CTR) measures the amount of users, who actually click on your ad upon seeing it on their display. The higher the CTR, the better for quality score improvement. The better your quality score, the higher the visibility and presence of your ads.
The CTR is calculated by dividing the total amount of clicks by the total number of impressions (the frequency of your ad being displayed).
The more precise your keywords, the better for your click-through-rate. A high CTR corresponds with a relevant and useful ad. If this is not the case your campaign needs to be optimized.