Anno Domini (), abbreviated as AD or A.D., defines an epoch based on the traditionally reckoned year of the conception or birth of Jesus of Nazareth. AD is also an abbreviation for Christian Era. Similarly, Before Christ (from the Ancient Greek "Christos" or "Anointed One", referring to Jesus), abbreviated as BC or B.C., is used in the English language to denote years before the start of this epoch.
See more at Wikipedia.org...