What is Google Adsense?
Google AdSense is an online advertising system run by Google. Its an opposite application of Google AdWords where advertiser from all over the world signup to create and show their ads on Google and its publisher sites.
Google places those ads on its search engine and millions of publishers sites who applied for Google AdSense.
Google does not charge anything to display these ads but only when someone clicks the ad.
For Example –
So if I applied for Google AdSense and Google shows its advertisers ads on my website then I will get paid for each and every click a visitor clicks on AdSense ads on my website.