A billennium is an event celebrated every billionth second from the time since 00:00:00, 1 January 1971. Unix enthusiasts have a history of holding at time_t parties, to celebrate significant values of the Unix time number.
At 01:46:40 UTC on 9 September 2001, the Unix billennium (Unix time number 1,000,000,000) was celebrated.
by Pachanka November 2, 2012