According to the Gregorian calendar, these distinctions fall to the year 2001, because the 1st century was retroactively said to start with the year AD 1.
The year 2000 is sometimes abbreviated as "Y2K" (the "Y" stands for "year", and the "K" stands for "kilo" which means "thousand").
[4][5] The year 2000 was the subject of Y2K concerns, which were fears that computers would not shift from 1999 to 2000 correctly.
However, by the end of 1999, many companies had already converted to new, or upgraded existing, software.
As a result of massive effort, relatively few problems occurred.