Basically CTR is stand for Click Through Rate. This is depend on how much Impression of your site / page (you can check it out in webmaster tool - differ search engine has different search tool)
Higher search engine better CTR, this is not so true for that we should optimized our title & meta description.
If we say that CTR is one of the signal than it's not false. one of the strongest element for benefical for ranking.
It is the ratio of total number of links on your ads with total impression (no. of times it is displayed) when someone conducts search on internet for the keywords you have targeted. It is one of the quality factor in improving your ad rank in sponsor listing.
Clickthrough rate (CTR)
A ratio showing how often people who see your ad end up clicking it. CTR can be used to gauge how well your keywords and ads are performing.
CTR is the number of clicks that your ad receives divided by the number of times your ad is shown (called impressions).
Each of your ads and keywords have their own CTRs that you can see listed in your account.
A high CTR is a good indication that users find your ads helpful and relevant. CTR also contributes to your keyword's Quality Score which can affect your costs and ad position.
You can use CTR to gauge which ads and keywords are successful for you and which need to be improved. The more your keywords and ads relate to each other and to your business, the more likely a user is to click on your ad after searching on your keyword phrase.