21H2

The abbreviation 21H2, meaning the second half of 2021 in the Microsoft semester scheme, can refer to multiple Microsoft Windows releases:
 * Windows Server 2022 (build 20348), released on 18 August 2021
 * Windows 11 (build 22000), released on 5 October 2021
 * Windows 10 November 2021 Update (build 19044), released on 16 November 2021

Windows as a service
 * Windows 10 Cobalt