The end of the Epoch in the Mayan calendar, the Winter Solstice in our current calendar but not the "first day of winter" in any proper calendar. The confusion results from the innumeracy of confounding period and point values. Events are points and seasons are periods.
That means we are but a scant 6 weeks from Imbolc or the First Day of Spring.The pagans and astrologers get this right and the Christians make amends by celebrating Candlemas the very next day. Conveniently, Candlemas is 40 days after Christmas just in time for the presentation of the baby Jesus at the temple.
For us, it is a good excuse to open up those seed catalogs and start planning the garden.