Armor encompasses items worn on different parts of a character's body to provide protection. It reduces the amount of physical damage you take from enemies.
Armor in Grim Dawn is localized. This means that when you receive a hit from an enemy, the game first rolls to see which armor slot will take the damage. It is thus important to be well equipped in all armor slots. (See Game Mechanics for more information on how armor works.)
All armor types have a Physique requirement in order to be equipped and have Light and Heavy sub-types, with heavy armor having a higher armor rating and Physique requirement. In addition, Head and Chest Armor also have a Caster type which has a Spirit/Physique requirement.