Trending is available to mobile in the US for Android. Support for iPhone and the rest of the world will come soon.
There are five different sections: Articles, In the story, Friends and Groups, Near the Scene, Live Feed.
Here is a video:
|Images copyright: Facebook newsroom|
|Facebook Inc Stock (NASDAQ: FB) - a screenshot from Google (disclaimers)|
|This is the first app's icon from Facebook with the Material design style|
|Image from newsroom.fb.com|
|Facebook down - a Screenshot of Facebook.com|