AdSense for Search is how Google includes search engine bit into the Google AdSense program. AdSense for Search can actually be termed as a sibling of Google AdSense program and is one great way of increasing website revenue for website owners. To implement AdSense for search, you just have to include the Google search box on your website. Again, Google offers the code that you need to use for including Google search box. You just have to paste the code at whatever place you deem as the most appropriate place for Google search box.
When your website visitors use Google search bar on your website, they get almost the same results as they would by using Google separately through Google.com. When these website visitors click the search results, the website owner earns revenue (CPC revenue). You can even include AdSense Ads on the search results page and earn CPM or CPC revenue from them. Also, you can customize the search results page to suit your websites theme. So, Google AdSense for search is one great way of making money just by including the Google search bar on your website. Besides that, the visitors to your website get an additional functionality through your website i.e. the facility to search the web using one of the most powerful search engine (without leaving your website).
AdSense for search is a great way of earning revenue through your website (and, in fact, one of the easiest ways too). A number of website owner actually use both the AdSense for Search and the regular AdSense for content in order to maximize their revenue.