The monk’s signature resource in Diablo III is Spirit.
Spirit powers many of the monk’s martial-arts skills, including abilities that generate or spend it during combat. Monk play therefore involves alternating between attacks that build Spirit and powerful techniques that consume it.
The resource system helps distinguish the monk from Diablo III’s other classes. The Barbarian uses Fury, the Demon Hunter uses Hatred and Discipline, the Wizard uses Arcane Power, and the Witch Doctor uses Mana. The Crusader, added later, uses Wrath.
Spirit should not be confused with the monk’s defensive or healing abilities. It is a combat resource rather than a separate health pool. The monk’s exact skill behavior can vary with runes, items, and set bonuses, but Spirit remains the class’s defining resource.