Mastery
Rule
Also Armor Mastery, Shield Mastery, Weapon Mastery
Mastery is an optional FeatFeat Feat · Tier 1Feats are abilities you buy with SP. you can take to gain ProficiencyProficiency TestProficiency is a Modifier showing your competence with certain Objects when used as intended. with an ArmorArmor Item · Armor · Tier 1Armor is a protective Object you wear to increase your Defense., ShieldShield Item · Shield · Tier 1Shields are Objects you wield to increase your Defense., or WeaponWeapon Item · Weapon · Tier 1Weapons are Objects you use to Attack., or to access a special ability it offers.
Source Player Codex