Yes it is an Operating System similar to Windows but it is a multi user
There are two types of Windows PC operating systems--Windows and Windows Server. The latest version of Windows Server now is Windows Server 2008 R2. The latest version of Windows (non-server) now is Windows 7.
Windows Server 2008
Server Core
The Microsoft Windows Server 2003 is software which is an operating system for computers. It was succeeded by Microsoft Windows Server 2008, and followed Windows server 2000.
Windows 2000 can be upgraded directly using Windows XP Professional or Windows Server 2003. The newest operating system in it's class is Windows Vista Business or Windows Server 2008, depending on whether you are using Professional or Server, respectively.
If the first word is supposed to be what and not when then the answer is Server Core.
Windows 2000, Windows XP, Windows Server 2003, Windows Vista, Windows Server 2008, and Windows 7 are all based on Windows NT technology.
Windows Server 2008, Redhat Linux, Solaris
Winodws XP
Initial Configuration Tasks
Windows Server 2008 was released in February 2008. The next operating system release is expected to be Windows 7 in October 2009.
Microsoft Windows Server 2008 represents a new integration of enhanced security, technical characteristic, management and its administration. It is based on the Windows operating system Vista with its features that it offers, however the 2008 version is the successor of the 2003 and the final product would be the mix of those two OS's. Microsoft Windows Server 2008 includes a great number of different technologies and services included within it. The best description of what does the 2008 version have to offer would be description of those features that make the 2008 system.