Christmas for Mexicans, in traditional homes and rural areas, is a religious holiday.  It is a celebration of the Nativity. This means the birthday of Our Lord Jesus. In order to prepare for the day of symbolic commemoration, we have the "Posadas". These celebrations are a "Novena" or nine days before the 24 which is the "Noche Buena" or "Holy Night".
http://www.nacnet.org/assunta/nacimnto.htm