AdSense is an ad serving application run by Google. Website owners can enroll in this program to enable text, image, and video ads on their websites. These advertisements are administered by Google and generate revenue on either a per click or per impression basis. Google also beta tested a cost per action service, but discontinued it in October 2008 in favor of a DoubleClick offering .In Q1 2010, Google earned US$2.04 billion ($8.16 billion annualized), or 30% of total revenue, through AdSense.
It is one of the major and best source of earning money for the webmasters.The money from AdSense can be made easily if you are good at seo and able to rank the website which in turn depends upon many factors.
Some people go for the Micro Niche.Niche here refers to the Internet Marketing term which means the topic around which your site will be around.The main concept in the Micro Niche is the keyword research phase of the seo.And having a exact match domain name to that of the keyword.We will discuss about it in details in seo section.