Unix billennium
The point in time one billion seconds after the Unix epoch: 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 "0" digit, erroneously sorted before earlier times starting with a "9" digit.
The name is not very logical as billennium should rather mean a billion years. Billesecum might have been a better term.
The word 'billennium' has also been used, presumably as abbreviated form of bi-millennium, for the year 2000 celebrations, by the Billennium Organizing Committee (BOC), who claims to own the term as registered trademark.
The word 'billennium' should not be confused with 'biennium', a period of two years.