Also known as Midwinter's Day, or Yule...
'Yule, is when the dark half of the year relinquishes to the light half. Starting the next morning at sunrise, the sun climbs just a little higher and stays a little longer in the sky each day. Known as Solstice Night, or the longest night of the year, much celebration was to be had as the ancestors awaited the rebirth of the Oak King, the Sun King, the Giver of Life that warmed the frozen Earth and made her to bear forth from seeds protected through the fall and winter in her womb. Bonfires were lit in the fields, and crops and trees were "wassailed" with toasts of spiced cider.'
From Celtic tradition.