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.
Anno Lucis
For example, a date Anno Domini (A.D.) becomes Anno Lucis (A.L.) 4000. This calendar era, which would designate 4001 BCE as 'year zero', was adopted in the 18th century as a simplification of the "Anno Mundi" era dating system used in the Hebrew calendar and borrowing from other ideas of that time regarding the year of creation.