What is "altbier"

n. A form of German top-fermenting beer that originated in Westphalia and later spread to parts of the Rhineland.

Altbier (German: old beer) is a style of beer brewed in the historical region of Westphalia and the city of Düsseldorf, Germany. Its name comes from it being top-fermented, an older method than the bottom fermentation of other lagered beers.