Contextual Marketing is what it sounds to be. On a website about the International food, you might have an ad for recipes, Chinese restraint or perfect food. On a website about Mobile Technologies, you might have an ad for Mobile accessories or used mobiles for sale. A Web Designing site might advertise a web hosting solutions or ready web templates...and a swimming site, swimming shoes. Contextual Marketing just means aligning the ad serving with the context/nature of the website and its audience, the same way like items are grouped in a shop. And the "context" can be cut much finer than website level, it can be page level, article level, or any level, so the ads always match the content they are appearing near, and thus, appeal to the interest of the visitor at any given moment.

So how you get into the picture and get use of google- adsense; the website publisher/owner? That's easy. Every time a visitor to your site clicks one of these ads, you make money. The better the ads are targeted, the more clicks you get, the more money you make. AdSense displays easy-to-read, text-based, relevant ads that don't overshadow the content of your website or annoy visitors. Actually, you have seen hundreds of these ads yourself, as you'll realize in a moment.

Today there are probably only a few places in your website that can directly make you money, if any. The magic of Google AdSense is this: It allows you to earn money through every page of your website. On top of that, with algorithms used to align ad content with page content Google automatically selects and displays ads for your website that are likely to generate the highest revenue for you.

And as defined by google :

Google AdSense is a fast and easy way for website publishers of all sizes to display relevant, unobtrusive Google ads on their website's content pages and earn money. Because the ads are related to what your users are looking for on your site, you'll finally have a way to both monetize and enhance your content pages.It's also a way for web site publishers to provide Google search to their site users, and to earn money by displaying Google ads on the search results pages.