Google Search Products, Adwords are the most common form of PPC advertising. Bing and Yahoo also have their own versions, though it seems that every day every social media site is coming out with their own versions of PPC marketing opportunities.
PPC stands for pay-per-click, a model of internet marketing in which advertisers pay a fee each time one of their ads is clicked. Essentially, it's a way of buying visits to your site, rather than attempting to “earn” those visits organically. Search engine advertising is one of the most popular forms of PPC.