'B.C.' originates from English as an abbreviation of the phrase 'Before Christ', where 'before' meant 'earlier than' and 'Christ' refers to Jesus Christ.

The dating system traces to medieval Latin usage such as 'ante Christum natum' ('before Christ was born'); English writers later used the phrase 'before Christ' and the abbreviation 'B.C.' for concise date notation.

Initially it referenced years counted backward from the believed year of Christ's birth; over time the abbreviation has continued to mark that era but is increasingly complemented or replaced by the secular term 'BCE' ('Before Common Era').