Year 2000. An abbreviation used to signify the problem that many operating systems Application programs will not work properly after the year 2000. This is because the programs have been written using 2 characters to signify the year (95,96,97 etc) - not taking the century into consideration. 00 will represent year 2000 the programs will process this year as if it occurs before any other (as 00 is less than 95).