The vambrace is a piece of defensive armour worn on the forearms. A modern term sometimes used to describe the same is lower cannon of the vambrace. These appear from the very early 14th century and possibly late 13th. Vambraces might be made of metal, leather or other materials depending on the period and location.
The term is also used to describe the combination of vambrace, couter and rerebrace when wearing full arm harness. In addition the English would use the term bracer to refer to the same. They differ from the modern bracer which is used to protect the internal forearm against 'string slap' (where the string of a bow hits the inside of the forearm).