If there is no alt tag, search engine doesn't understand anything from the image.
That's why you should use alt tag on your all pictures, which you use in your website.
The "Sites Linking In" count shows the number of sites that Alexa found that link to this site.
If a site has Certified Metrics instead of estimated, that means its owner has installed code allowing us to directly measure their traffic.
Each computer has to have an IP number to connect with other computers. On the off chance that you have site that have high fame, both you are gone to by more guest and you pick up high benefit on promotions that you show.
Certified Site Metrics are metrics that are directly-measured from the website instead of estimated.
Bounce Rate (%) Percentage of visits to the site that consist of a single pageview.
Daily Pageviews per Visitor Estimated daily unique pageviews per visitor on the site.