Abbreviation referring to a 32-bit Operating System
created by Microsoft Corporation. It's based on the Mach Microkernel and part of VMS. It has no native DOS support; only DOS emulation. NT stands for "New Technology". Often, the word "Windows" will be used before "NT". i.e. Windows NT 4.0 Workstation.
Windows 2000 is basically just NT 5.0.