What exactly do B.C. and A.D. stand for? B.C. stands for “Before Christ,” as in Jesus Christ. It indicates the number of years before the birth of Jesus (although Jesus himself was born in 4 B.C.). A.D. stands for the Latin phrase Anno Domini. That translates to “In the year of our Lord.” It’s used to mark years after the birth of Jesus. Considering the Gregorian calendar was created by a pope of the Catholic Church, it makes sense that it tells time according to the birth of Christianity’s main religious figure.

Source: Wonderopolis