Christmas season

The Christmas season lasts from Christmas Day until the Feast of the Baptism of the Lord.

December 25	Christmas Day
January 1	Octave of Christmas; Solemnity of Mary Mother of God
December 25 - January 6	Twelve Days of Christmas
January 6	Epiphany
Sunday after Epiphany	Baptism of the Lord

Xmas

The first letter of this ancient abbreviation is not the English character "X" but the Greek character Chi. It is the first letter of "Christos" in Greek: Χριστος. People who use this abbreviation (as I did in the pie chart of the liturgical year) are not "Xing" Christ out of Christmas; they are going back to the original language of the New Testament and to the earliest days of Christianity to find a convenient symbol for Christ.