ADabbreviationAnno Domini (used to indicate that a date comes the specified number of years after the traditional date of Christ's birth).
Usage
ADshould be placed before the numerals, as inAD 375(not375 AD). The reason for this is thatADis an abbreviation of Latinanno domini, which means ‘in the year of our Lord’. However, when the date is spelled out, it is normal to writethe third century AD(notAD the third century). Compare with BC.