AD or A.D. after a year is the shortcut for theLatin expression "anno domini" and mean in the year of (Jesus) Christ. AD therefore means years after the birth of Christ. E.g. Barrack Obama was elected President of the United States of America 2008 AD.
On the contrary if a year is meant to be before the birth of Jesus Christ the year got the appendix BC or B.C. which means before Christ. Obviously the year in that case means years until Jesus Christ was born so if e.g. the battle of hysiai took place in 669 BC this does mean it took place 669 years before jesus christ was born.
By the way, there is a fantastic article to that theme in wikipedia.com . Read it for further information.
Anno domini: in the year of our lord
Active Duty. (Military term)
advance
Please explain what you mean by "ad."
It's German for purely ad
AD means Anno Domini
To/for/from/by mother
well
After death
To the fishpond.
to or towards
To his sister
closed.
ad is multiplex address data line bus