The version number is a date, which helps decode the various major updates to Windows 10. Each of these are essentially doing a whole OS upgrade, Microsoft has really stepped up their installer/upgrade technology to make this pretty painless and hidden behind the scenes. They are pretty close to macOS upgrades these days as far as ease of upgrading, but as Doug discovered, they can still break some software.

1507 = July 2015 (Initial release)
1511 = November 2015 (November update)
1607 = July 2016 (Anniversary update, added the Linux subsystem)
1703 = March 2017 (Creators update)

The month tends to be when the Windows Insiders (opt in beta testers) receive the near final version of the new iteration. Microsoft is aiming for one of these major updates per year. And they get rolled out in batches once released.