The term anno Domini is Medieval Latin and means "in the year of the Lord"  but is often presented using "our Lord" instead of "the Lord",   taken from the full original phrase " anno Domini nostri Jesu Christi ", which translates to "in the year of our Lord Jesus Christ ". This calendar era is based on the traditionally reckoned year of the conception or birth of Jesus, with AD counting years from the start of this epoch and BC denoting years before the start of the era. This dating system was devised in by Dionysius Exiguus of Scythia Minor , but was not widely used until after It is often directly contrasted to the more ancient, Anno Mundi AM conferring "in the years of the world" which recounts the ages based on biblical tradition beginning with the Creation account. To this day, it is firmly observed through virtually all Jewish religious sources, some minor non-Jewish orthodox societies, and is a reference in many aged and restituted manuscripts. The Gregorian calendar is the most widely used calendar in the world today.
Common Era CE is one of the year notations used for the Gregorian calendar and its predecessor, the Julian calendar , the world's most widely used calendar era. The expression has been traced back to , when it first appeared in a book by Johannes Kepler as the Latin : annus aerae nostrae vulgaris year of our common era ,   and to in English as " Vulgar Era". Since the later 20th century, CE and BCE are popular in academic and scientific publications as culturally neutral terms. They are used by others who wish to be sensitive to non-Christians by not explicitly referring to Jesus as " Christ " nor as Dominus "Lord" through use of the other abbreviations. The year numbering system used with Common Era notation was devised by the Christian monk Dionysius Exiguus in the year to replace the Era of Martyrs system, because he did not wish to continue the memory of a tyrant who persecuted Christians. This way of numbering years became more widespread in Europe with its use by Bede in England in Bede also introduced the practice of dating years before what he supposed was the year of birth of Jesus,  and the practice of not using a year zero.