Pay Per Click search engines offer a service in which you purchase ads that show up at the top, side or below the search results for the specific keyword phrases you bid on. The highest bidder for a chosen keyword normally ranks highest in the search engine results. The price of the bid is charged to the advertiser every time a user clicks on the advertisement.
Advertising positions that shows in the search engine listing result are separated from the main natural search results and are generally labeled as "sponsored link " or "featured link " .
In March 2004, Yahoo announced their new Overture Site Match(tm) program that combines PFI with PPC.However, they still offer their traditional PPC sponsor ad program, but they no longer offer a simple PFI program. Now, if you want to speed up your inclusion in Yahoo directories and its search properties and partners (currently AltaVista, FAST, Yahoo and some of MSN), you'll have to pay a fee for each URL that you want included, plus 15 or 30 cents (depending on your category) for every click through to your site.