The Y2K problem. A term 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).