The Office 365 link

The Office 365 link immediately follows the Waffle. This link allows you to get back to the Office 365 Home page if you ever want to go back to it for whatever reason. Most users decide to configure their settings to start the day in the portal at a different point than the Office 365 Home page, but they may need to get back to Home for several reasons. One reason could be to access software downloads easily as this is one of the elements that is easy to access from Home rather than from within an application.

Following the Office 365 link may be an indicator of where you are in Office 365:

For instance, in the previous screenshot, you are in SharePoint. After the words Office 365, you can see the words SharePoint. In SharePoint's case, this is clickable and will lead you to the SharePoint home page.