Passive skills, or just Passives, are a type of character skill in Diablo III which benefits the player without the need for active control over it. Passive skills are unlocked when characters reach level 10, at which point a few skills become available for selection and the first Passive skill slot unlocks. Passive skills must be equipped in a specific slot to function, similar but using completely separate slots from active skills. Passive skill benefits range from statistical increases, to improvement to specific active skills, to completely original effects.
Each class has different passive skills, sometimes emphasizing their unique qualities, other times similar to each other. As more levels are gained, additional Passives and slots are unlocked, until over a dozen individual skills are available and can be selected into four slots (three prior to the Reaper of Souls expansion). The order skills are selected is completely unimportant - they all function to full effect as long as they are selected.
All classes have a Passive which grants some sort of direct protection from death, usually with a 2 minute cooldown. These are highly prioritized by Hardcore characters for obvious reasons. Other common skill categories include life increases or regeneration, resource recovery or cost reduction, increased damage, increased defenses or Damage Reduction, and crowd control.
A fifth Passive can be used by equipping a Hellfire Amulet. This legendary item's unique power is to provide the player with a specific Passive skill, which is determined randomly when the item is crafted. Several crafting attempts may be required to get a desired Passive skill, but of course, any one of the five desired skills will do, with the remaining four selectable from the Skills screen normally.