This is a helper variable that abbreviates the Software\Microsoft\Windows NT\CurrentVersion registry path. It is used by other variables to retrieve system information.
You can refer to this variable as <WinCurVerNT>. Because it is a partial registry path, it is typically used as <@<HKLM>\<WinCurVerNT>\...additional path...>. Do not change its value; it has been carefully configured for cross-platform compatibility.