What's Adsense

I don't think there is any one who doesnot know this Answer But Still..

Adsense is an ad serving application run by Google Inc. From this program Blog/Website Owners can earn money by showing advertiser's ads.

Google Describes it Better:-

What's AdSense?

The flexible, hassle-free way to earn revenue online

• Get paid for displaying targeted Google ads on your site.
• Customize ads to match your site's look and feel.
• Track your success with online reports.
• It's free!

Source: Google