According to wikipedia a jack boot is:
tall winged leather cavalry boots, which had been "jacked" or reinforced against sword blows by use of chain mail sewn into the lining of the leather. The wings on these high boots particularly protected a rider's knee-joint from a sword blow. ... The term originates from the French word Jaque (m) meaning chainmail. The term is of Catalan origin, descended from the Arabic schakk.The second meaning of the term is ... a combat boot designed for marching, rising to at least mid-calf, with no laces, typically a leather sole with hobnails, and heel irons. The Germans call this boot "Marschstiefel", meaning "Marching Boot". This is the classic boot used by the German Infantry and the "Stormtroopers" in World War I
