"Sponsored Links" are sites that come from companies that pay the search engine to have their sites appear when certain terms are being searched.  They are "paid listings" and often should be seen more as advertisements. 

Many search engines place such listings in an obvious way.  The listings are usually shaded or placed in a separate category.  Sometimes they are listed first and you have to scroll down to find the regular listings.  Sometimes they are listed on the left, right, or bottom of the page.

Above is an example of a search results screen from Google.  The search entered was "health care coverage."  Sponsored Links appear both on the top and the right.  Not until the shade disappears, on the left, does the first regular search result appear.  For research purposes, the Library recommends you avoid these "sponsored categories" and that you go directly to the regular listings. 

Unfortunately, some search tools like the Yahoo! search engine will also place paid listings as regular search engine listings.  You will not be able to know if they are paid to be there.