Pauldron generally refers to any kind of shoulder-pad style armor, covering the top of the shoulder. The armpit proper is usually covered by someting called a rondel, although the pauldron may extend all the way down, limiting the extent of movement, something that is characteristic of Italian or Milanese armors.

Paul"dron (?), n. [See Powldron.] Mil. Antiq.

A piece of armor covering the shoulder at the junction of the body piece and arm piece.

© Webster 1913.