PPC advertising stands for Pay per Click advertising. It is centered around paying the website publisher money each time someone clicks on the ads. Advertisers usually bid on keywords. Some keywords are more expensive for advertisers and hence more profitable for publishers when users click on them.
Some people build websites around high valued keywords in Google Adsense in order to make more money. What they have to realize is many of these keywords are high bid because there is low demand for clicks and because of the competitiveness of the industry. So you might get more money per click, but so few people click on them and/or visit these kind of websites, your overall profits will be less.
For example mesothelioma is a very high priced keyword in many PPC networks. If you build a website centered around mesothelioma you probably will have a hard time even getting a lot of traffic to your website because there will be so many websites out there trying to take advantage of this high bid keyword. To make matters worse there will be few people even looking at these types of websites in the first place, because not too many people are suffering or know anyone suffering from mesothelioma.
