Facebook added a search tool about a year ago, but it wasn’t very useful. Now, Facebook search returns results for all public posts. This means that when you search for something on Facebook you will get results from your timeline, your friends’ timelines, and any public posts.
This makes it easier to look at how much conversation there is around a particular topic. You can gain deeper insights into who’s talking about the things that matter to you.
This is a great tool for those of us who are looking for people to connect with on Facebook, but it does raise privacy concerns. You do have control over what is searched, and here’s a great video to explain the options.