Because Christmas is a joyful holiday celebrated by people of all backgrounds and nationalities, it is considered appropriate to say "Merry Christmas" as a polite greeting during the Christmas season. The phrase "Merry Christmas" is derived from the Old English words "Meere Crīstmasse," which means "Mass of Christ." It is a customary greeting in many English-speaking countries, including the United States, and is a way to express goodwill and good wishes to others during the holiday season. In contrast, "Happy Christmas" is more commonly used in countries like the United Kingdom and Ireland.