Y2K 
(wī′t-kā)
(wī′t-kā)adj.
1. Of or relating to the year 2000.
2. Of or relating to a defect in the code of a computer program caused when a year is represented by its last two digits only and the program interprets that year as falling inclusively between 1900 and 1999 instead of between 2000 and 2099: Y2K compliance; Y2K testing.
[Y(ear) + 2K, informal expression for the number 2000 (using K, symbol for 1000).]