The initial version of Windows version 1709 'Fall Creators Update' was released on October 17, 2017. Since then, Microsoft has released a few feature updates for the Windows 10 OS family, including version 1803 and version 1809; and subsequently a bunch of cumulative updates, including security fixes and stability improvements. Today, Windows version 1709 has exited mainstream support.
As you may already know, the next major update to Windows 10, code named "Redstone 3", recently got its official name. Microsoft revealed that it will be called "Fall Creators Update". Now, it appears that Microsoft has referenced the version number for the Windows 10 Fall Creators Update in related documentation.