Hello,
Thank you for posting in Microsoft Community forum.
Based on the description, I understand your question is related to Semi-Annual channel , Annual channel and LTSC.
Semi-Annual channel: The Semi-Annual Channel releases are supported for 18 months and a new release will be out twice a year.
Annual channel: Releases of Windows Server in the Annual Channel typically occur every 12 months.
Long-Term Servicing Channel (LTSC): continues to have 5 years of mainstream support and 5 years of extended support, with a new release planned for every 2-3 years.
You can run winver to check current machine's version details, and below are Microsoft documents about the Semi-Annual channel, Annual channel and LTSC.
Windows 10 and Windows Server 2016 update history - Microsoft Support
Windows Server Semi-Annual Channel - Microsoft Lifecycle | Microsoft Learn
Windows Server servicing channels | Microsoft Learn
Have a nice day.
Best Regards,
Molly