The Google AdSense blog announced they are now using the query data in the referrer URL to better target and match the AdSense ads on your web site. Basically, if you go to Google, type in a query, click on a site that has AdSense on it, Google will use the query you entered on Google (or any search engine) to match the ads to the query and the contextual nature of the page.
Supposedly, Google has been doing this for a while. I think that is news to me. But what Google said they recently changed was now storing the query for a few hours, so if you visit other sites with AdSense on it, hours later, it will continue to use your search history to match the AdSense ads on third-party web sites. Of course, Google said you can opt out of this.
Let's assume the user in our example leaves your golf website and browses through to a news website that is also an AdSense partner. Since [golf shop atlanta] is in a referral URL that was visited in the past few hours, we may use those query words, along with the content of the news webpage itself, to determine the most relevant ad to show the user on the news website.
Google supposedly also emailed publishers about this change, but publishers did not understand it, from what I take.
Forum discussion at WebmasterWorld.