The German phrase "zwischen den Jahren" ("between the years") refers to the days between Christmas Eve and New Year's Day or - depending on who you ask - the 6th of January (Epiphany).

So, if your German friends don't answer the phone or open the door during that period, please remember:

They are spending their holidays in a non-existing time-slot between 2 consecutive years.

Enjoy our language!

#TheGermanWord

@jensclasen
Imho stems from Roman times: the "Iden des März" did not count into any of both years
@hias1234 @jensclasen My specialty is law and religion of the Roman Republic. Sorry, what?
@holothuroid
This is what we have learned in school. You have other information? Please explain
@jensclasen