Windows NT
In short: Windows NT is a Microsoft operating system (1993).
In more detail: Windows NT (New Technology) is the operating system line with its own kernel on which all modern Windows versions are based.
In Depth
Details
NT 3.1 appeared in 1993, NT 4.0 in 1996. Features: NTFS, user rights, stability. See Windows 2000, Windows XP.
See Windows, Microsoft, operating system.
See also: Windows, Microsoft, Operating System (OS)