Armor is a form of physical protection first applied to individuals, then later ships and structures.
Klingon uniforms typically included body armor.
The Kalar of Rigel VII wore armor. Captain Christopher Pike, later speaking about his experience on this planet, said to Doctor Philip Boyce that he should have sensed trouble when he saw the swords and the armor. Instead, he became trapped in a fortress and had to fight one of the Kalar warriors. (TOS: "The Cage", "The Menagerie, Part I")