Anno Domini (sometimes found in the irregular form
Anno Domine), abbreviated as
AD or
A.D., and
Before Christ, abbreviated as
BC or
B.C., are designations used to number years in the
Julian and
Gregorian calendars. The
calendar era to which they refer is based on the traditionally reckoned year of the
conception or
birth of
Jesus, with
AD denoting years after the start of this
epoch, and
BC denoting years before the start of this epoch. There is no
year zero in this scheme, so the year AD&_160;1 immediately follows the year 1&_160;BC.
The Gregorian calendar, and the year numbering system associated with it, is the calendar system with the most widespread usage in the world today. For decades, it has been the unofficial global standard, recognized by international institutions such as the United Nations and the Universal Postal Union. It is also a basis of scholarly dating, though some people adopt the Common/Christian Era labels, retaining the same numeric values but using the label "CE" (Common/Christian Era) instead of "AD", and "BCE" (Before the Common/Christian Era) instead of "BC".
The term Anno Domini is Medieval Latin, translated as In the year of (the/Our) Lord.[1][2]782 It is sometimes specified more fully as Anno Domini Nostri Iesu (Jesu) Christi ("In the Year of Our Lord Jesus Christ").
Traditionally, English has copied Latin usage by placing the abbreviation before the year number for AD; since BC is not derived from Latin it is placed after the year number (for example 64&_160;BC, but AD&_160;2009). However, placing the AD after the year number (as in "2009&_160;AD") is now also common. The abbreviation is also widely used after the number of a century or millennium, as in "4th century AD" or "2nd millennium AD" (although conservative usage formerly rejected such expressions).[3]
