What is the full form of AD
AD: Anno Domini
AD stands for Anno Domini. It is a Medieval Latin term. It means "in the year of our lord". This term is used to represent the year after the Christians God Jesus Christ. Sometimes AD is also spelled as After Death which is totally wrong. Actually, this is a misconception because AD and BC both are used to represent years count individually, and BC stands for Before Christ. So many people misunderstand this term.
AD was discovered by a Monk named Dionysius Exiguus. It had replaced the Diocletian era that had been used in old Easter table. Dionysius Exiguus created this term to determine the correct date for Easter as directed by the Pope St. John I. Prior to this method, the other methods which were used to find the date for Easter led to the confusion, e.g. a 532 year calendar cycle that originated in Alexandra era.
The main purpose of BC/AD is to create a dating system which can make the birth of Jesus Christ the dividing point of the world history. However, it is believed that Jesus was not born in 1 AD, it was around 6-4 BC when he was born. So, according to this dating system, 500 BC means 500 years before Jesus was born. And, 2000 AD means around 2000 years after Jesus was born.
The Julian and Gregorian calendar uses AD and BC as a designation to label number of years. AD is used to specify the start of the Epoch and BC specifies before the start of the Epoch. In recent times, the term BC and AD are replaced by B.C.E and C.E where B.C.E means "Before Common Era" and CE is used to denote "Common Era".