A non-GUI small footprint version of Windows Server introduced with Windows Server 2008. All interaction is via the command line. Server Core was designed to provide essential services and also lower exposure to hacking.
The next server version, Windows Server 2012, allowed switching between the GUI interface and command line, and it added .NET support. Windows Server 2012 R2 added Windows Defender for greater security.
Windows Server 2016 introduced Nano Server, another small footprint server version designed for cloud operation and remote management instead of the GUI/non-GUI Server Core approach. Windows Server Version 1709 turned Nano Server into a container-based product (see Windows Server 2016
). See Windows Server 2008
and Windows Server 2012