google adsense side job brings profit

AdSense is an ad serving application run by Google Inc. Website owners can enroll in this program to enable text, image, and video advertisements on their websites. These advertisements are administered by Google and generate revenue on either a per-click or per-impression basis. Google beta tested a cost-per-action service, but discontinued it in October 2008 in favor of a DoubleClick offering (also owned by Google).[2] In Q1 2010, Google earned US$2.04 billion ($8.16 billion annualized), or 30% of total revenue, through AdSense.[3]
data source : http://en.wikipedia.org