The minimum length of time that the player needs to wait after using an ability before they can use it again. This concept was first introduced by the text MUD Avalon: The Legend Lives. An analogy can be made to the reload time and firing rate of weapons. For example, a machine gun has very fast firing rate, so it has a very low cooldown between shots. Comparatively, a shotgun has a long cooldown between shots. Cooldown can be used to balance a weapon such as a turret-mounted machine gun having infinite ammunition, since it can only sustain continuous fire until reaching a threshold at which the weapon would have to cool down (hence the term) before it could be fired again. In design terms, cooldown can be thought of as an inverted ‘casting time’ where instead of requiring a wait time before using an ability, cooldown may replace casting time and put the wait after the ability is activated. This creates a new dimension to the balancing act of casting speed versus power: ‘lower cooldown, faster cast, but weaker strength’ versus ‘higher cooldown, slower cast, but greater strength’. This mechanic is integral to such games as World of Warcraft, where cooldown management is key to higher-level play and various abilities deal with cooldown (for example, cooldown reduction or immediately finishing cooldown on certain abilities). From the technical point of view, cooldown can also be used to assert control over frequency of cast in order to maintain a fluid frame rate and ping. For example, in the game Diablo II, cooldown was added in the form of a patch to several graphically and CPU-intensive spells to solve the problem of extreme lag caused by players spamming (ie: repeatedly casting at maxed out cast rates) these spells in multiplayer games. Moves and attacks in fighting games (like those from the Street Fighter series) are measured in animation frames (which may be 1/20 to 1/60 of a second per frame). Each move has a certain number of frames in which it is considered to be ‘recovering’ before another move can be executed, which is similar to cooldown in concept. However, there is no player control over the character during recovery frames, and the character can not perform any movement or attacks until fully recovered. Because the character is vulnerable during recovery, strategic use of skills is necessary to make sure the opponent cannot immediately counter the player-character.