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 use the Outlook app on your mobile device, you have probably already used this feature.
Focused Inbox will replace the Clutter feature, however if you have the Clutter feature turned on, the folder will remain.
For more detailed information on Focused Inbox, see Focused Inbox for Outlook