Pay per click (PPC) is an Internet advertising model, rather to say that this is a program used on search engines, advertising networks, and content websites, where advertisers only pay when a user actually clicks (this means that being interested he/she clicks) on an advertisement (ad) to visit the advertisers' website.

Every time when a visitor click on an ad which is published by the publisher (who takes the responsibility to market the product of an advertiser or simply publish ads for the advertiser) a commission is paid to publisher according to the program. This phenomenon is called Pay per click.

 An advertiser analyses their target customer or target market & bid on keywords depending upon their product. These keywords help the publisher to fetch relevant ads where these ads are running. 

Although many pay per click providers exist, Google AdWords, Yahoo! Search Marketing, and Microsoft adCenter are the largest network operators as of 2007.

Pay per click campaigns can be generally categorized into two major categories: sponsored match (or keyword) and content match.

Sponsored match:     Campaigns involve the display of ads on search engine results pages.

Content match:          Campaigns involve the display of ads on publisher websites, newsletters, and e-mails.

 There are other types of pay per click programs that target product or service searches and product comparison sites.