The Free On-line Dictionary of Computing (30 December 2018):

Windows XP
XP

    The version of the Microsoft Windows
   operating system that, when it was released on 2001-10-25,
   finally merged the Windows 95 - Windows ME strain with the
   Windows NT - Windows 2000 one.  XP comes in two main
   versions: Windows XP Professional Edition and a simplified
   subset for home users, Windows XP Home Edition.

   Windows XP home page (http://microsoft.com/windowsxp/).

   (2009-08-12)