Windows Server 2008 - Definition from the Hotspot Shield Glossary
Historically Microsoft has released a standard operating system for businesses and individual use, and a server operating system in conjunction that is specifically used for running servers. Windows Server 2008 is an update to Windows Server 2003 R2 and was superseded by Windows Server 2008 R2. This server OS uses the same basic features and code as Windows Vista so has much of the same functionality.
Aside from the features of Vista, Server 2008 also features several server tools including Server Manager, Windows System Resource Manager, Hyper-V, and Failover Clustering. Generally Windows Server 2008 was favorably received by the computing world due to its enhanced functionality and revamp of such services like Active Directory.