Basically a Windows 10 phone-sized full computer that has docking features that make it conceivably the singular computing device in your life that covers all mobile and desktop contexts.
[1] https://www.windowscentral.com/microsoft-bring-back-courier-...
Unfortunately, it seems like Microsoft has given up on Windows Phone already.
[1] http://www.zdnet.com/article/microsofts-x86-on-arm64-emulati...
Beyond that, rumor has it that Microsoft hopes selling tablets/laptops with ARM will open the Windows ARM space enough in the meantime while the Windows team is finishing the next version of key Windows shell components (nicknamed the "Composable Shell" or CShell), which would be make the Continuum experience for say Phones stronger because instead of switching entirely different shell applications (start menu, taskbar, et al) between form factors, the same applications responsively adapt themselves.
https://www.theverge.com/2016/12/7/13866936/microsoft-window...