n. Shortened form of Windows 2000, a new operating system from Microsoft that is expected to ship either in late 1999 or early 2000.
Given that we are fully expecting there to be the ongoing raft of post-release service packs, it's not unreasonable to describe beta 3 as a slightly undercooked version of W2K aimed at people who don't mind things a bit chewy for a few months.
—Jon Honeyball, “In the Countdown to Windows 2000, Is Beta 3 Going to Be the One to Watch?,” Network News, April 07, 1999
Dear Mr. CIO: Your life is difficult enough already. You're grappling with the ever-alarming Y2K, the ever-later W2K (Windows 2000) and a variety of other crises.
—“Why IT execs should pay close attention to Linux,” Computerworld, March 08, 1999
1999 (earliest)
Microsoft is faltering in court and its key "industrial-strength" Windows 2000 project is two years behind schedule.

In a wicked turn of phrase, the magazine says investors may face a W2K problem from the Windows delay in Y2K.
—Stephen H. Dunphy, “The Newsletter,” The Seattle Times, February 19, 1999
Thanks to Gareth Branwyn, Wired magazine's Jargon Watcher, for the head's up on this one.
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