millennium bug

Informal.
  1. a bug that can cause computers or software to misinterpret the first two digits of the year 2000 as 19, due to the coding of dates using only the last two digits of the year.

Origin of millennium bug

1990–95
Also called Y2K problem, Y2K bug.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for millennium bug

millennium bug

noun
  1. computing any software problem arising from the change in date at the start of the 21st century
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012