The term AD stands for Anno Domini, which is a Latin phrase that means “in the year of our Lord.” It refers to the system used by historians and Christians to date events from the birth of Jesus Christ. The use of this calendar began in 525 CE when Dionysius Exiguus, a Scythian monk, proposed it as a way to replace the Roman calendar which was based on the reigns of emperors. AD is used along with BC (Before Christ) to indicate years before and after Jesus’ birth.