an armor plate that protects the arm.

A brassard is a piece of cloth or other material worn around the upper arm. The brassard, when spread out, may be roughly rectangular in shape, where it is worn merely around the arm; it may also be a roughly triangular shape, in which case the brassard is also attached to a shoulder strap. It is used as an item of military uniform to which rank badges (or other insignia) may be attached, instead of to the actual clothing.