The
civil calendar is any
calendar in use in any country at any point in time which is used for civil, official or administrative purposes. All dates referred to by people in that country are expressed in relation to this calendar.
The Gregorian calendar is most widely used in the world. By all points it is the de facto international calendar. Though that calendar is associated with the Catholic Church and the papacy, it has been adopted by many countries, as a matter of convenience, which are secular or non-Christian. Some countries still use the Julian calendar, while others still use other calendars.
It is not uncommon for another calendar, or even more than one, to be running in parallel to the civil calendar. For example, Christian Churches to have their own calendars, which they use for their own festivals; though most of these dates are then expressed in relation to the civil calendar. In Christian terminology these festivals are called movable feasts. Very few Christian festivals are fixed in relation to the civil calendar, the most notable one being Christmas.
The same applies to Jews and to Muslims, who have their own calendars for religious purposes, but which are then expressed in terms of civil calendar dates.
