Google’s advertising network. Relevant advertisements can be placed near content on a site and the publishers that place that ad there will share the profit from the ad clicks with Google.
Similar to the AdSense from Google but centers it attention on keyword focused ads. The ads are keyword targeted and are sold on a “cost per click” basis in an auction which factors in ad clickthrough rate and even the max bid.
This gives merchants the opportunity to expand their reach by paying independent agents on a cost per action basis.
This is a rank that helps measure traffic of a particular website.
One of the original powerhouses in search but once they updated their algorithm it caused them to remove a lot of websites and this caused them to lose a lot of their power in the search world.