The frog-mouth helm (or Stechhelm meaning "jousting helmet" in German) was a type of great helm, appearing from around 1400 and lasting into the first quarter of the 16th century. The helmet was primarily used by mounted knights for tournaments (jousting) rather than on the battlefield.
The frog-mouth analogy was drawn from the way the ocularium (the slit through which the wearer of the helm could see) resembles the open mouth of a frog. During jousting tournaments, the helmet offered a better degree of protection from lances that would splinter after impact with the rival's body armour. Early examples of the stechhelm were made from a single piece of metal, while later dated helmets had hinged constructions that could be disassembled.