The couter (also spelled "cowter") is the defense for the elbow in a piece of plate armour. Initially just a curved piece of metal, as plate armor progressed the couter became an articulated joint. Couters were popular by the 1320s.[1]
Oakeshott, R. Ewart (1996) [1960]. The Archaeology of Weapons: Arms and Armour from Prehistory to the Age of Chivalry. Mineola, New York: Dover Publications. ISBN978-0486292885.