Mulled wine or Glühwein is wine (usually of the strong/robust red variety) that has been slowly simmered (cooked over a low heat) for a long time with various spices such as nutmeg, cloves, cinnamon, vanilla any many others. It might also include citrus and/or fruit juice(s) and sugar may or may not be added. Pieces of fruit as slices or diced pieces are sometimes included.
It almost invariably contains alcohol (the heating is not so severe as to drive all of it off, and anyway, it can also be fortified with spirits or more wine) but non-alcoholic varieties are also available for those adults who are driving and also for kids.
It is usually drunk in the winter time and especially at Christmas, and is very popular in Germany, Austria & France.
Mulled cider is also common and made in a similar way.