Google AdSense happens to be an Affiliate Marketing Program unlike any other. You see there are allot of Affiliate Marketing Programs out there that let you earn commission through their advertisement on your website.
But Google AdSense is little different then the others because its a hack of allot more advanced then others!
For example Allot of the affiliate marketing programs out there are allot more annoying and difficult then Google AdSense!
Because I bet allot of times when you visit a website you see allot of Advertising Banners and who in the world would click on them if they are nothing related to the subject of the website that you are on!
Pretend that you are on a website that talks about Games but the Advertising Banner on the site is toward Furniture would you click on it? Of course not! I know I wouldn't!
Google AdSense can Sense the content of your website and if you are talking about games the advertising will be about games, if you are talking about Music the advertising will be about music!
Google AdSense works through Google AdWords because every time someone tries to advertise their business they create their advertising through Google AdWords and it ends up being displayed through Google AdSense on many websites related to the subject of their advertising!
So it's not just affiliate marketing but its really TARGET MARKETING!