Office 365 Groups, in a nutshell, provides internal team collaboration on specialized or generalized subjects. One could say it is an expanded version of distribution lists. One could also say, it helps to lower the noise generated by reply-all emails.
The official word from Microsoft is that “Groups brings together People, Conversations, and Content across Office 365. By providing an integrated experience that link together email conversation, file storage, and calendar even management. Groups create an integrated experience for teams to focus on group activity. Groups can be public to enable information sharing within your company, or private for teams that deal with sensitive subjects.”
Groups can be accessed from the Outlook Web App or from the new Outlook 2016 application.
All messages are displayed in a list view, as shown below:
Files can also be stored and discussed in Groups:
For more information on how this works, see this post.
Groups also help you keep track of group events. This calendar can be shown side by side your personal calendar, inline, or you can add the events to your personal calendar.
Groups for Office 365 is a powerful addition to Office 365. It is one which I think will change the way groups and team interact within the organization.