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.
Global traffic ranks of 100,000 are subject to large fluctuations and should be considered rough estimates.
If a site has Certified Metrics instead of estimated, that means its owner has installed code allowing us to directly measure their traffic.
Site owners who install the Alexa Certify Code on their website can choose to display their Certified Metrics, such as Monthly Unique Visitors and Pageviews, if they wish.