Facebook is testing a new feature with a limited number of users.
Users can star a group of friends which are most important to them.
Facebook would make sure that you get updates from them on their newsfeed on a priority basis.
It is a known fact that Facebook tends to hide most of the updates from your friends if you are following a lot of people.
They use a relevancy factor to showcase the important updates. This star feature would let you highlight the important friends to ensure that most updates are delivered in your timeline.