Question

AD
 ( or chiefly US   A.D.)  abbr  
  — used to refer to the years since the birth of Christ
   550 A.D. = A.D. 550
   the first century A.D.
   in the year 823 A.D.
  ◇ A.D. stands for the Latin phrase anno Domini, which means “in the year of the Lord.” compare B.C., B.C.E., C.E.