Christmas is a Christian festival celebrating the birth of Jesus.
The English term Christmas (“mass on Christ’s day”) is of fairly recent origin. The earlier term Yule may have derived from the Germanic jōl or the Anglo-Saxon geōl, which referred to the feast of the winter solstice. The corresponding terms in other languages—Navidad in Spanish, Natale in Italian, Noël in French—all probably denote nativity. The German word Weihnachten denotes “hallowed night.”
Since the early 20th century, Christmas has also been a secular family holiday, observed by Christians and non-Christians alike, devoid of Christian elements, and marked by the exchange of gifts. In this secular Christmas celebration, a mythical figure named Santa Claus plays the pivotal role. (Source)
The Christmas Proclamation, as provided in the translation of the U.S. Conference of Catholic Bishops:
The Twenty-fifth Day of December,
when ages beyond number had run their course from the creation of the world,
when God in the beginning created heaven and earth,
and formed man in his own likeness;
when century upon century had passed since the Almighty set his bow in the clouds after the Great Flood,
as a sign of covenant and peace;
in the twenty-first century since Abraham, our father in faith, came out of Ur of the Chaldees;
in the thirteenth century since the People of Israel were led by Moses in the Exodus from Egypt;
around the thousandth year since David was anointed King;
in the sixty-fifth week of the prophecy of Daniel;
in the one hundred and ninety-fourth Olympiad;
in the year seven hundred and fifty-two since the foundation of the City of Rome;
in the forty-second year of the reign of Caesar Octavian Augustus,
the whole world being at peace,
JESUS CHRIST, eternal God and Son of the eternal Father, desiring to consecrate the world by his most loving presence, was conceived by the Holy Spirit, and when nine months had passed since his conception, was born of the Virgin Mary in Bethlehem of Judah, and was made man:
The Nativity of Our Lord Jesus Christ according to the flesh.
(Source)