Windows Server is a brand name for a group of server operating systems released by Microsoft. It includes all Windows operating systems that are branded "Windows Server", but not any other Microsoft product. The first Windows server edition to be released under that brand was Windows Server 2003. However, the first server edition of Windows was Windows NT 3.1 Advanced Server, followed by Windows NT 3.5 Server, Windows NT 4.0 Server, and Windows 2000 Server; the latter was the first server edition to include Active Directory, DNS Server, DHCP Server, Group Policy, as well as many other popular features used today.
Windows Server operating system releases under the Long Term Servicing Channel are supported by Microsoft for 10 years, with five years of mainstream support and an additional five years of extended support. These releases also offer a complete GUI desktop experience, along with GUI less setups such as Server Core and Nano Server for releases that support them.