Shorthand for the year 2000, it came to mean specifically the potential difficulty that corporate, governmental, and financial computer systems might have encountered if programming changes were not made. Before 2000, many computer programs allocated space for only two digits in the year instead of four (98 meant 1998, 99 meant 1999, and so on). Once Jan. 1, 2000 arrived, computers would have read the year as 1900 and potentially wiped out data or locked-up computer systems.