zwischen den Jahren

Etymology
lit. 'between the years'.

Adverb

 * 1) the time around Christmas and New Year, with different precise understandings:
 * 2)  between Christmas and New Year: December 27 to 31
 * 3)  from Christmas Eve through New Year: December 24 to January 1
 * 4)  from Christmas Eve through Epiphany: December 24 to January 6
 * 5)  during the Christmas vacation: maximally December 21 to January 8 (depending on the year and jurisdiction)