What is 1 AD?

The year 1 AD was the first year of the common era in the parts of the world that use the Gregorian calendar. According to New Advent, the dating convention was devised by Saint Dionysius Exiguus in the 6th century as a Christian replacement for the previous Era of Diocletian.

Dionysius Exiguus oriented his calendar so as to fix the birth of Jesus Christ in the year 1 AD. Unfortunately for this dating convention, according to Wikipedia, there eventually developed a consensus among scholars that the event would have taken place four to six years earlier than St. Dionysius had assumed.