Pay per Click(PPC)
Pay-per-click text ads, such as Google Ad Words, are an advertising medium that a local marketer can afford to test once they understand the options available. When it comes to paying for advertising, you want to get people who are most ready to buy. That means you can restrict your ads from showing up in searches, for example, from computers outside of your geographic area.
Google has a specific web crawler, the MediaBot, which downloads web pages. The job of the software behind the crawler is to analyse the pages and reduce them to prioritised keyword lists. When the ad unit code on a specific page is loaded, the software compares the keyword list associated with the page with a ranked list of ads to serve for those keywords.