Search Retargeting
Have you ever wondered how search engines know exactly what you’re looking for? How they know what advertisements to appeal to you personally? Search engines typically show ads related to the search criteria. If someone searches for jump ropes, chances are that the search engine will display ads for toy stores and a local boxing gym along with the typical search results. This way the search engine makes money from advertisements and companies can market their products.
Results pages are displayed by using algorithms to determine the best fit for the search. This is based on relevance from the search criteria and popularity of a certain link. As in, the website that is visited the most based on similar searches usually ends up at the top of the page. For advertisements, it works a little differently. Since most advertisements are paid, which one shows up first depends on how much the company paid to have their ads put up. Mostly, the position of the ad gets sold using an auction process. Nowadays, however, search engines are developing more complex algorithms to determine which ads to show. This is also called “search retargeting” where they use your other open tabs to see what products might interest you, not just ones related to what you searched for. Although this keeps in mind your privacy, especially if you are looking for something personal. This may seem invasive but they do not keep any of the information that you provide and companies get better profits from the advertising.
http://www.ecommerce-guide.com/article.php/3807541/Yahoo-Using-Search-Behavior-to-Target-Display-Ads.htm