Bouche is actually a common French word for mouth. In the English language it means an opening in a shield to accommodate a spear. The bouche would thus be a mouth in the shield from behind the safety of which a spear could be maneuvered, thus combining the two functions of offence and defense. A Bouche was specifically a notch cut in the top part of the shield.
The concept of having a bouche in ones shield got popular only after the fifteenth century. This can be attributed to the sport of jousting where charging knights could safely rest their lances on the notch in the corner of their shields. The concept was not new. The Greek hoplites with their extended spears perhaps also used something similar. Surely Achilles must have maneuvered his spear forward and back through the bouche in his shield during his dance to the death with Hector. The practice probably went out of fashion with the rise of Rome and her legionnaires armed with broad swords and not spears.
The concept of having a bouche in ones shield got popular only after the fifteenth century. This can be attributed to the sport of jousting where charging knights could safely rest their lances on the notch in the corner of their shields. The concept was not new. The Greek hoplites with their extended spears perhaps also used something similar. Surely Achilles must have maneuvered his spear forward and back through the bouche in his shield during his dance to the death with Hector. The practice probably went out of fashion with the rise of Rome and her legionnaires armed with broad swords and not spears.