A click-through rate (CTR) refers to the proportion (rate) of visitors to a page who follow (click through) a particular link on that page.
Examples
In search engine marketing (SEM), click-through rate (CTR) often refers to the percentage of users who click a link to a web page that is listed within search results (clicks) against how often that particular webpage has been displayed in the search results (impressions).
Click-through rates can also apply to clicking a ‘buy now’ button on a product page, therefore analysing your CTRs can be a key component in measuring your sales conversions.
Examination of CTR to identify query type
The click-through rates observed for any given term can be used by search engines to determine whether it is navigational or informational/transactional. For instance the top organic result will have a higher click-through rate on a navigational search whereas the click-through rates of informational/transactional searches are distributed more evenly.
Once search engines have determined what type of query is being searched they can adjust the SERPs accordingly. For example a query like ‘what is the time in london’ is such a closed informational query that google doesn’t even display any links within the SERPs for this query.
Use of CTR and bounce rates to predict site quality
High CTR in search results tells search engines that a site may deserve to rank higher, however this may also be due to clickbait titles & descriptions. Therefore these sites with high CTRs are identified and their bounce rates are examined to see if bounce rate is low, in-keeping with high quality sites that deserve to rank highly, then if both these measures are satisfied the ranks begin to climb. This is the basis for modern SEO which focuses on user experience rather than linkbuilding, due to the power that CTR and bounce rates have in overriding traditional link equity-based ranks.