Microsoft's Windows 10 operating system for personal computers has been said to be the "last version of Windows". First released in July 2015, Windows 10 has been updated on roughly a semi-annual basis with "feature updates" - changes or improvements to the functionality or user interface of the operating system.
The latest version of Windows 10 - Version 1903 - has been slowly pushed out to computers over the past few months. Version 1903 was initially planned to be released in March 2019, but suffered some reliability problems and was delayed to May 2019.
Versions of Windows 10 have been identified by a 4-digit year and month of initial planned release - i.e. 1809, 1803, and so on going backwards to the original version of 1507. However due to frequent release delays, a new versioning system is expected to take effect with the next version of Windows 10 this fall. Subsequent versions are expected to be identified by the 4-digit year and half-year of planned release - i.e. 19H2, 20H1, and so on going forward.
For more information about the history of Windows 10, including changes that were made in the eight versions to-date,