Paid search is when online advertisers bid on search engine or search directory queries and pay a fee whenever someone clicks on their online ad. In essence, the highest bidder on a particular keyword has its ad show up first on the list. For example, go to Google.com and search for "fishing supplies." The "sponsored links" in the right hand column (such as "basspro.com") are paid search ads.
As of 2005, paid search is about a $5 billion market and is expected to double by 2010 (according to Park Associates). When it comes to Internet advertising success, audience reach is the most important factor. The more visitors to the site, the more opportunity to generate revenue. Also as of 2005, Yahoo has the top audience, with 103.8 million unique visitors in November, followed by MSN with 96.1 million visitors, according to Nielsen/NetRatings. Google is third, with 85.5 million visitors.