Defending X for Y amount of time is a common objective type found in both single-player and multiplayer games. Such objectives appear in many action and strategy-based genres. In basic terms, the objective requires the player to defend something, whether it be an NPC, item, or location on a map for a specific amount of time. The players must prevent a location from being reached by enemies, an object from being stolen from behind them and taken to a second location, or an object or objects from running out of hit points. Players must often face increasingly difficult opponents and/or an increasing number of enemies as time progresses. Enemies will frequently spawn infinitely until the objective is met. The objective is commonly deployed in horde modes.