This day is known as the Feast of Seven Fishes for many Italians who will customarily have a dinner of seven fishes in honor of the seven Sacraments and seven days of Creation.
The 1917 Code stated for all Latin Rite Catholics in Canon 1252:
§ 1. The law of abstinence alone is to be observed on all Fridays.This Tradition of Fasting is still observed in the Byzantine Tradition. I quote:
§ 2. The law of abstinence and fast together is to be observed on Ash Wednesday, the Fridays and Saturdays of Lent, the Ember days [all day], and on the Vigils of Pentecost, the Assumption, All Saints, and the Nativity.
§ 3. The law of fast alone is to be observed on the other days of Lent.
§ 4. On Sundays and days of obligation the law ceases except on a feast of obligation during Lent; and the vigils are not anticipated; likewise the law ceases on Holy Saturday at noon.
The Christmas Fast, in preparation for the feast of the Nativity on December 25, is one of the minor fasts of the Church. This fast of forty days was introduced in the 12th century. Counting back 40 days from the feast of the Nativity, the fast begins on the evening of November 14 - the feast of the holy apostle Phillip. As a result, it is traditionally called Phillip's Fast or the Phillipian Fast (in Slavonic, Filipovka).Source: Byzantine Catholic Archeparchy of Pittsburg
This fast is not penitential, but is rather a fast of preparation, like the pre-Communion fast. By abstaining from certain foods, we are opening up a "space" in our lives through asceticism and obedience, into which God may enter.
One final day of strict fasting awaits us. Normally, this would be the Vigil (in Greek, Paramony) of the Nativity, December 24. But Saturday and Sunday are never days of strict fasting in the Byzantine Rite (with the single exception of Great and Holy Saturday). So when December 24 falls on one of these two days, the day of strict fast is anticipated on Friday.
On this day, a special service called the Royal Hours is celebrated. This service consists of the daytime services of the First Hour, Third Hour, Sixth Hour, Ninth Hour, and Typika, celebrated with special psalms and readings for the Nativity. (This service is called royal because, at one time, the Emperor himself always attended the service.) Each part of the service has an Old Testament prophecy, an Epistle reading, and a reading from the Holy Gospel.
The Vigil of the NativityFinally, we have come to the very eve of the Nativity - the Paramony or Vigil of Christmas (December 24). If it is a weekday, it is a day of strict fasting, with the Royal Hours celebrated during the day, and Vespers and the Divine Liturgy of Saint Basil in the evening.
If December 24 is a Saturday or Sunday, the Divine Liturgy may be celebrated in the morning, and we sing the troparion of the Vigil:
At that time, Mary registered in Bethlehem with the elder Joseph, who was of the house of David. She had conceived without seed and was with child; and her time to give birth had come. They found no room in the inn, but the cave became a pleasant palace for the Queen. Christ is born to raise up the likeness that had fallen.The fast is not quite over; if there is a meal or Holy Supper in the evening of December 24, after Vespers, it is a meatless one. But we have arrived at the feast of the Nativity of our Lord, God and Savior Jesus Christ.