A calendar date consisting of all like digits; i.e. month, day and at least the final two digits of calendar year are comprised of similar numbers. (Digits fall so that the numeric date will be repetitive.)
Superstition surrounds such dates in many cultures and religious/occult practices. The dates can be seen as being either good or bad omens, but most seem to consider the dates lucky or auspicious.
The last complete mono date of this decade will be 12/12/12 and will be the last mono date, or near mono date for at least a decade. After 2020, there will be combinations such as 02/20/20, but an absolute repeat will not occur again for a century.
Examples: Sept. 9'th 1999 - 9/9/99
Jan. 1'st 2001 - 01/01/01
Feb. 2'nd 2002 - 02/02/02
and so on.
Next mono date from time of this posting:
Nov. 11, 2011 - 11/11/11