Microsoft Windows Server User CAL 2012 Volume licence
Microsoft Windows Server User CAL 2012 is a user-based access license for Microsoft Windows Server. CALs (Client Access Licenses) are no longer included with Windows Server 2012 Datacenter and Standard, which is why you'll need additional licenses for access.
Contrary to device CALs (device licenses), Microsoft Windows Server User CAL 2012 provides an user with access to Windows Server.
Microsoft Windows User CAL 2012 is downgradable. For example, you can run it in combination with MSMicrosoft Windows Server 2008.