Answer:
"Merry Christmas"
Chag Molad Sameach
חג מולד שמח
Chag basically means holiday or "festival." Molad generally means "birth." And Sameach basically means "happy." Thus the literal translation is "happy birth festival" (celebrating the birth of Jesus Christ).
I don't know who answered the above, but Jews don't celebrate the birth of Jesus! See all the other answers for the correct meaning regarding the birth of the new moon each month.