AdSense is an advertising program which enables website owners, bloggers, and writers to earn money online without spending any. Placing AdSense advertisements on websites or blogs will result in revenue for the owners of these sites.
Advertisers pay Google to run their advertisements on websites that Google finds fit for this purpose, and Google obliges. The advertisers pay Google and Google shares this revenue with those on whose websites or blogs these advertisements are placed by them.
AdSense is run by Google Inc and is thus referred to often as Google AdSense. If you own a website or a blog, free or hosted, you can apply for to Google for an AdSense account. When they approve your sites to host Adsense advertisements, you become an AdSense publisher.
The system works in such a way that the advantages to the advertiser, publisher, and Google are equally distributed. AdSense advertisements appear on websites in the form of clickable text links which briefly describe the product advertised.
If the text attracted the attention of the viewer and if he wanted to learn more he clicks on the link and the website that represents the product advertised launches where the interested viewer can have access to all the information on the product advertised.
The click is registered by google and the advertiser is charged a fee agreed upon previously.
Google shares this revenue with the website owner or blogger on whose site this advertsioement appeared and was clicked on by a viewer.
Obviously, it follows that the more exposures the website has, the more chances there are for ads to be clicked on and the more ads that are clicked on, the more AdSense revenue for the publisher.
However Google has taken all the precautions against cheating and have the necessary software to detect unauthorised clicks. Unauthorised clicks mean the site owner clicking on his own ads in order to generate more revenue for himself.