Year zero
Year zero does not exist in the anno Domini system usually used to number years in the Gregorian calendar and in its predecessor, the Julian calendar. In this system, the year is followed by . However, there is a year zero in astronomical year numbering (where it coincides with the Julian year ) and in ISO 8601:2004 (where it coincides with the Gregorian year ) as well as in all Buddhist and Hindu calendars.
Year Zero (political notion)
The term Year Zero ( "chhnam saun"), applied to the takeover of Cambodia in April 1975 by the Khmer Rouge, is an analogy to the Year One of the French Revolutionary Calendar. During the French Revolution, after the abolition of the French monarchy (September 20, 1792), the National Convention instituted a new calendar and declared the beginning of the Year I. The Khmer Rouge takeover of Phnom Penh was rapidly followed by a series of drastic revolutionary de-industrialization policies resulting in a death toll that vastly exceeded that of the French Reign of Terror.