Sponsored Links (also called Paid Listing, Paid Inclusion, Paid Placement, etc.)
Remember search engines are commercial entities trying to make a profit. Many search engines include links that companies have paid for to appear when you use certain keywords. The links can be either in the results list or in the page's border. Sometimes they are clearly marked but more often they deliberately blend into your results.
For more information see Danny Sullivan's article, "Buying your Way In: Search Engine Advertising Chart" from the web site SearchEngineWatch.