The data is for the past 12 months, updated monthly.
The "Sites Linking In" count shows the number of sites that Alexa found that link to this site.
For more information please see this explanation of how Alexa determines the number of sites linking in.
The website owner has installed an Alexa Certify Code on the pages of their site and chosen to show the metrics publicly.
Not all websites implement our on-site analytics and publish the results.
These metrics have a greater level of accuracy, no matter what the ranking.