There was buzz around "Trending Topics" at the end of 2013. Facebook introduced this feature which was in the testing mode. Now the feature is launched successfully. 
The trending news and updates all around the world is displayed in the News Feed section where people can go through the news and share it or give their comments on. 
Now News Feed will not only display the trending posts of your friends and connected people but it will have a platform for other important stuff from around the world. 
As discussed in the earlier post, the feature will show the topics that are based on factors that include your interests and the post's that you comment on etc. Mainly the feature will act according to the interests of users. 
By clicking on the topics or trending posts, you will open the door to the article based news. So, that's "Trending Topics" feature.