Focused Inbox is a new feature coming to Office 365. Focused Inbox helps you take control of your inbox and focus on the emails that matter most. It will separate your inbox mail into two tabs -- Focused and Other.
This is coming to all versions of Outlook to give you one consistent view of the important items in your inbox. If you are using Outlook app or Office 365 OWA, this feature is already available.
Focused Inbox will replace the Clutter feature, however if you have the Clutter feature turned on, the folder will remain. Eventually, the Clutter feature will no longer work.
For more detailed information on Focused Inbox, see Focused Inbox for Outlook