For reference, an outline of what constitutes the holiday season. A complicated matter, since there’s both a secular and a religious notion in this domain, and the two are intertwined.
The secular season begins, in the U.S., the day after Thanksgiving (this year that’s today) and lasts through New Year’s Day. (Elsewhere, the beginning of the season is less clearly defined, though things are pretty clearly underway by December 1st.)
The religious season begins, in Western Christianity (the dates are somewhat different in Eastern Christianity), with the first Sunday of Advent (this year that’s November 27th). The season comes in three pieces:
Christmastide, from Christmas Eve through January 5th, with Christmas (Day), December 25th, as its centerpiece (the secular holidays of New Year’s Eve, December 31st, and New Year’s Day, January 1st, fall in there, as does St. Stephen’s Day, December 26th, and the solstice — the winter solstice in the Northern Hemisphere, the summer in the Southern — on December 21st or 22nd, the 22nd this year);
and Epiphany, or Twelfth Night, January 6th.
In counterpart to these occasions, there’s Hanukkah (this year, from sunset on December 21st through sunset on December 28th) and Kwanzaa (December 26th through January 1st).
And in addition to the religious season (a technical notion) and the secular season (an ordinary-language notion), there’s what you might call the commercial season, the period of advertising, selling, and buying before Christmas and of after-Christmas sales; and of what you might call the public-celebration season, characterized by holiday movies and tv shows, holiday lighting, the playing of holiday songs, holiday parties, exchanges of greetings, performances of The Nutcracker and The Messiah (and in some places, Beethoven’s Ode to Joy), holiday food and drink, and so on. Both the commercial season and the public-celebration season are fuzzily defined, but tend to take in longer periods than the religious and secular seasons.