Wikipedia
Federweisser (also Federweißer , from German Feder, " feather", and weiß, "white"; from the appearance of the suspended yeast), is an alcoholic beverage, typically 4 percent alcohol by volume, but it's not uncommon to see Federweißer in the region of 10 percent alcohol by volume. It is the product of fermented freshly pressed grape juice, known as must. The term in principle includes all stages of fermentation from must to finished wine.
It is known as Suser, Sauser, Neuer Süßer (new sweet), or Junger Wein (young wine) in Southwest Germany, Switzerland and South Tyrol, Fiederwäissen in Luxembourg, Sturm (storm, from the cloudy appearance) in Austria, Federweißer in Bavaria, Neuer Wein (new wine) in the Palatinate, Bremser in Franconia, burčiak in Slovakia, burčák in Czech Republic, vin bourru or vernache in France, must in Romania, must or karcos in Hungary, "მაჭარი" (machari) in Georgia, "մաճառ" (machar) in [Armenia].
(Note that, in Switzerland, this same term has a completely different meaning. There, Federweisser refers to a white wine made from red grapes, typically pinot noir.)