Rauhnächte (engl. Yuletide or Twelve Days of Christmas, Twelvetide, Christmastide):
Also called "Rauchnächte", "Zwölf Nächte", "Glöckelnächte", "Innernächte", "Unternächte". Originally being a germanic festival it later underwent a christian reformulation. The "Rauhnächte" fall between Christmas and Epiphany, i.e. 24/25 December and 5/6 January. In some regions the Feast of St. Thomas the Apostle, 21 December, winter solistice (or midwinter), is considered the first night of the "Rauhnächte", and is thus closer to the germanic origin of these holidays. The name of these nights refers to the use of "Weihrauch" (incense) during this time to ward off evil spirits.
There are various customs, traditions, and festivities associated with these nights. A summary of these in English is found here.