Personalised results are inflenced by your online social network.
If you are logged in to a social network while searching (Facebook for Bing, or logged in to Google with your Gmail Google Account), you could see results from or inflenced by your social circle.
In Bing, for instance, results can include indications of what your friends have previously liked or shared via Facebook.
On Google, you might be more likely to see your friend’s blog for relevant searches.