My late father, Benito F. Legarda, used to tell us that the correct term for the dawn Masses of Christmastime was Misas de Aguinaldo (Christmas Masses).
Misa de Gallo is the midnight Mass on Christmas Eve. The dictionary of the Real Academia Española defines Misa de Gallo as the Mass celebrated on Christmas Eve.
Somehow in this country, Misa de Gallo came to be popularly applied to all the simbang gabi at Christmastime.
—BENITO LEGARDA JR.