Focused Inbox is a new feature of 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 for Windows, the Outlook mobile 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. Beginning January 31, 2020, the Clutter feature will no longer work. It is also currently being deactivated for those users with low usage (less than 12 emails per month being moved to the Clutter folder).
For more detailed information on Focused Inbox, see Focused Inbox for Outlook