PPC, or Pay-Per-Click search marketing…
…is any paid campaign through a search engine or network that only charges you when a user clicks on your ad.
The king daddy of all PPC campaign platforms is Google Adwords, followed by Yahoo Search Marketing, MSN AdCenter and others like Ask Sponsored Listings, MIVA, etc.
I have been managing PPC campaigns for several years, going back to the time when Yahoo Search Marketing was Overture and Overture was Goto.com. I have achieved conversion rates as high as 15%-25%.