In the olden days, Microsoft’s support policy for Windows and Office was simple. Each release had five years of mainstream support, during which it received security updates, feature improvements, and stability fixes. That was followed by five more years of extended support, during which time it received security updates only.
With Windows 10 and “Windows-as-a-service,” that policy got all shaken up. After a period of refining the details, Microsoft settled on the current scheme. Mainstream Windows, Office, and Windows Server users are on the Semi-Annual Channel (SAC). They get two major servicing updates each year, with each version named with a two-digit year, two-digit month; the current version is 1709 because it was built in September 2017. Its successor will be built in March 2018, hence named 1803. Each of these releases receives 18 months of security updates, and each Office SAC release is only supported on supported Windows SAC releases.
For organizations that can’t or won’t use the SAC, there is also a Long-Term Servicing Channel (LTSC). Windows, Office, and Windows Server LTSC releases are made every three years and receive the traditional five years mainstream plus five years extended support policy.
Source:: Arstechnica – Gadgets