What is PPC?
Pay-Per-Click is a paid form of advertising, popularized mostly by the "search engine" Overture (formerly GoTo). The concept is fairly simple. Businesses bid to be placed at or near the top of the search results for particular keyword phrases. The bidding is done on a "per-click" basis, meaning that a company pays a specific amount every time the engine sends them a visitor. In addition, the top results on Overture also show up in the results of many of the popular search engines (usually listed as "sponsored" or "featured" results). Google has a similar version of PPC (AdWords Select) that has taken over some of the engines that used to display Overture results (most notably AOL Search).
Pay-Per-Click campaigns have some advantages over traditional search engine optimization. First of all, they require no changes to a current site's content or look to obtain top positions, just a willingness to pay. Also, the implementation of a pay-per-click campaign is relatively quick- it can take just a few minutes to start getting targeted traffic, versus sometimes months for standard SEO campaigns. Finally, unlike search engine optimization, the implementation of a PPC campaign is relatively easy and does not necessarily require any specialized knowledge (although experience with search engine marketing and keyword research is a definite advantage).
Of course, there are limitations to this type of advertising. New bids can lower the positions of other firms, and many will react by raising their bid to regain a previous ranking. Monitoring of positions becomes crucial. These campaigns can also become prohibitively expensive, depending on the competitiveness of the keyword phrases and the aggressiveness of the competition. In addition, many of the "savvier" search engine users have learned to recognize PPC results as paid advertising and bypass them without consideration.