The common abbreviation "A.D." (Anno Domini) means "Year of the Lord," i.e. after Christ's birth. Some twentieth century scholars prefer the abbreviation "C.E." or "Common Era." Standard usage seems to be moving back to "A.D." and "B.C." (Before Christ), perhaps because they are more concise and clear than the phrase "Before Common Era" (BCE).
See the article in Wikipedia: http//en.wikipedia.org/wiki/Common_Era