Primarily used in Christian contexts to refer to the celebration of Christ's birth. Often appears in the fuller phrase キリスト降誕祭.
See also: キリスト降誕祭 (キリストこうたんさい)
I attended the Christmas Mass at church.
Christmas is celebrated on December 25th.
celebration of a saint's or great person's birthday
Rare, extended use; can refer to the birthday celebration of any saint or revered figure, not only Christ.
This church also cherishes the celebration of saints' birthdays.