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The computer term Y2K refers to the "Year 2000" bug, or Millennium Bug, a flaw in legacy computer systems that could have caused major disruptions when the calendar rolled over from December 31, 1999, to January 1, 2000.

The origin of the Y2K bug

During the early years of computing, data storage was extremely expensive. To save memory, programmers used a two-digit shortcut for the year (e.g., "98" for 1998). They assumed the software they wrote would be replaced long before the turn of the century and didn't account for what would happen when the year changed from '99 to '00.

The potential problem

The Y2K bug was a problem of interpretation, where computer systems could have misinterpreted "00" as the year 1900 instead of 2000.

The resolution: In the years leading up to 2000, extensive global preparations were made to fix the problem. Programmers worked to identify and update old code, an expensive and time-consuming process. In the U.S., the government created the President's Council on Year 2000 Conversion to coordinate efforts.