Pay per click (PPC) is a form of online advertising that is used to direct traffic to a website, where the advertiser pays an ad publisher each time a user clicks on their ad and is directed to their site. The most common form of PPC advertising is on search engines (Google Adwords and Microsoft Bing dominate this market). In that case, ads are served to users based on the keyword or search query they have entered. There are many other sites where PPC advertising is used (Facebook, Instagram and LinkedIn to name a few). On these social sites, ads are shown to users based on selected audience targeting.