* People you’re connected to through social services that you’ve listed in your Google profile, such as Twitter and FriendFeed.
* People in your Gmail (or Google Talk) chat list.
* People in your Friends, Family, and Coworkers contact groups for Google.

If someone you don’t know shows up in your social search results, it’s likely that they’re connected to someone you do know. Social Search includes results from public connections of your immediate social circle, since there’s a high likelihood that you know them as well. For example, if you’re following someone on Twitter, and that person is following five other people, those five other people are also included in your social circle.