Pay-per-click is an internet advertising model, where advertisers and hosts agree upon a certain amount only when their ad is clicked. With search engines, advertisers typically bid on keyword phrases ,which are of utmost importance to the web market. Host sites commonly charge certain price per click This price can be a fixed or it can be obtained through bid system.In fixed rate system,the agreement between the two parties is on fixed amount.While in bidding system, the advertiser signs a contract and he has to compete with other advertisers in an auction,where each advertiser informs the host of the maximum amount that he or she is willing to pay for a given ad spot,usually using online tools to do so.This auction carries out as and when the ad is trigerred.