AdSense has launched site-flavored AdSense for Search, which enables publishers to have their rearch results “flavored” to the theme of their site.
Here is an example of how it works, according to the AdSense blog:
For example, if you’ve got a site about music, over time our search results might learn that when your users search for [bass], they mean the instrument – not the fish.
With AdSense contextual targeting, it would normally use other words on the page to know whether bass was referring to an instrument or a fish. However, with search, a search engine wouldn’t neccessarily know which option was the one the user was searching for. But using site-flavored would “teach” AdSense over time for the search.
To use site flavored, you do need to regenerate your AdSense for Search code by checking off the “‘Flavor my search results to my site'” box when generating the ad code.