AdSense is a word which is known for everyone who want to earn money online. AdSense is an ad serving application run by Google Inc. Website owners can enroll in this program to enable text, image, and more recently, video advertisements on their websites. It is the most popular pay per click ad network you can find.

Though AdSense is the most popular way of earning money online, AdSense TOS is very strict and banned publishers for their mistakes. Specailly they don't forgive about invaild clicks. So AdSense publishers always need to follow their TOS.

You can apply for AdSense if you have a website or a blog but getting approved is becoming harder and harder. They don't take brand new sites anymore so you need to apply for AdSense with site which is at least few months old. It would take 1 day to a week to get a reply from AdSense.