Cooldown
A CD or cooldown refers to the time a user must wait before repeating a recently completed action. Cooldowns are used in video games for balancing purposes. Cooldowns help ensure that players cannot spam the same action repeatedly, which would be unfair to other players, and difficult to transmit over the Internet.
Effect on gameplay
Cooldowns also enhance gameplay for the player, by encouraging decision-making and planning. For instance, if an ability can only be used once every 90 seconds, it should be used judiciously, because of the wait time. The player must anticipate what will happen next, and weigh the advantage of using the ability immediately, against the "penalty" period when the ability is "on cooldown."
In strategy and collaboration
Cooldowns may be strategically conserved to coincide with one another, to gain advantage or survivability at critical gameplay moments. For instance, when defeating a boss in World of Warcraft, a group of players may "blow their cooldowns" (activate several cooldown abilities as soon as possible). If timed correctly, this strategy maximizes the effect of their actions for a brief moment. If timed incorrectly, however, those abilities will be unavailable until their respective cooldowns reset. In this way, cooldowns enhance the rewards of group coordination, and familiarity with the nuances of the game.
How long can a cooldown be?
Cooldowns in video games range from less than a second, to several hours or days. For example, World of Warcraft has a GCD (global cooldown) of one second for most character actions, and a 15 or 30-minute cooldown to return to the player's inn. In early versions of World of Warcraft, the Paladin ability "Lay on Hands" incurred a 60 minute cooldown, or 40 minutes if improved with talents. Some profession abilities, such as transmuting precious metals, incurred a 96-hour (four-day) cooldown, which affects prices in the in-game economy.