Unix billennium
The Unix Billennium is the point in time represented by a Unix time value of 109: 01:46:40 UTC on September 9 2001. Some programs which stored timestamps using a text representation encountered sorting errors, as in a text sort times after the turnover, starting with a "1" digit, erroneously sorted before earlier times starting with a "9" digit. Affected programs included the popular usenet reader KNode and email client KMail, part of the KDE desktop environment. Such bugs were generally cosmetic in nature and quickly fixed once problems became apparent.
The Unix Billennium is sometimes described as "109 seconds after the Unix epoch". This is not quite correct, because Unix time is not a purely linear count of seconds. "109 non-leap seconds after the Unix epoch" is closer to being accurate, but the epoch is in 1970 and leap seconds weren't actually defined before 1972.
The name is an amalgamation of "billion" and "millennium", recalling the year 2000 bug. The name is not very logical as billennium should rather mean a billion years. "Gigasecond" would be a more apt term.
The word "billennium" is also used by such writers as Madeleine L'Engle (A Wind in the Door) and Stanisław Lem (Imaginary Magnitude), apparently in reference to a billion years.
The word "billennium" should not be confused with "biennium", a period of two years.