Passive ability

A passive ability is an ability that is always active and doesn't require user interaction to use. Usually, they are not shown in your spellbook or tooltips, but some are. Many talents and racial traits are passive abilities. They are sometimes known as an innate ability. Passive abilities on items or mobs are sometimes called powers.

• Most item bonuses and buffs are passive abilities like "+5 Strength" or "Improves your chance to hit with spells by 1%".
• Many talents add passive abilities like the Safe Fall rogue ability (reduces damage from falling).

• Miners get Toughness (mining) (adds HP based off of the skill level).
• Skinners get Master of Anatomy (increases critical strike based off of the skill level).
• Alchemists get Mixology (any potion an alchemist can create has double duration and extra strength).

With the release of Patch 4.0.1, when a character chooses a class specialization, they automatically get related passive abilities.

• Paladins, Warriors, Hunters, and Rogues get Parry at various levels; Death knights start with it.
• Paladins, Warriors, Shamans get Block (must have a shield equipped).

• Dwarves have Gun Specialization Your chance to critically hit with Guns is increased by 1%) and Frost Resistance (reduces the chance you will be hit by frost spells by 2%).
• Gnomes get Expansive Mind (increase intellect by 5%, Arcane Resistance (gnome racial) (Reduces the chance you will be hit by Arcane spells by 2%), and Engineering Specialist (15 point skill bonus to Engineering).
• Humans have The Human Spirit (increase spirit by 3%, Diplomacy (10% bonus to faction point gains), Will to Survive (Removes all movement impairing effects and all effects which cause loss of control of your character), Sword Specialization (Expertise with One-Handed Swords and Two-Handed Swords increased by 3, and Mace Specialization (Expertise with One-Handed Maces and Two-Handed Maces increased by 3).
• Night elves get Quickness (dodge chance increased by 1%), Wisp Spirit (become a wisp when dead with 75% movement speed increase), Nature Resistance (racial) (reduces chance to be hit by Nature spells by 2%), and Elusiveness (Reduces the chance enemies have to detect you while Shadowmelded or Stealthed).
• Orcs have Hardiness (increase resistance to stun effects by 25%), Command (pet melee damage increased by 5%), and Axe Specialization (increases expertise while using axes by 5).
• Tauren get Endurance (max Health increased by 5%), Cultivation (15 point skill bonus to Herbalism), and Nature Resistance (racial) (reduces chance to be hit by Nature spells by 2%).
• Trolls have Regeneration (increase health regeneration bonus by 10%; also allows 10% of normal health regen during combat), Beast Slaying (5% damage bonus to Beasts), Throwing Weapon Specialization (increase Throwing Weapon skill by 5), and Bow Specialization (increase Bow skill by 5).
• The Forsaken get Underwater Breathing (underwater breath duration increased by 233%) and Shadow Resistance (racial) (reduces chance to be hit by Shadow spells by 2%).
• Everyone gets Dodge (Gives a chance to dodge enemy melee attacks).