Cooldown

The term cooldown is defined as a period of wait time before a spell, ability, or item power can be used after a prior spell, ability, or item power. Often referred to by the pseudo-acronym "CD".

'Cooldown' may refer to:
 * The period of time after using a spell, ability or item before it can be used again. Many powerful spells and abilities have lengthy cooldowns, encouraging players to exercise forethought in choosing the best moment to use them. Some abilities have no cooldown and can therefore be used as often as desired (provided any other requirements are met).
 * The period of time after using almost any spell or ability in which it is not possible to use any other spell or ability. This is known as the global cooldown, and prevents players from using several abilities at once, instead requiring them to be used one at a time (often as part of a 'rotation'). Most abilities cause and are affected by the global cooldown, but some are not - see the list below.
 * An ability with a lengthy cooldown; for example, Save your cooldowns for boss fights.

Shared cooldown
A shared cooldown is when some spell, item or ability prevents usage of certain others while it is cooling down. It effectively applies the same cooldown to all those that it shares a cooldown with.

It is important to know if a spell or item has a shared cooldown, since that is much more limiting than an isolated cooldown. This usually means that you must choose wisely which to use, since you cannot use all within a short time period. For instance, many potions share cooldowns with other potions; the warrior abilities Heroic Strike and Cleave share a cooldown; and so do hunter traps.

A shared cooldown need not match the ability's individual cooldown; some powerful abilities with lengthy cooldowns also have a short shared cooldown with similar abilities, preventing a player from gaining several powerful effects at once.

Warrior stance changes also fall under the shared cooldown category. Switching stances as a warrior prevents switching to another stance for 1.5 seconds but does not prevent the user of other abilities.

Some abilities do not have shared cooldowns, but still prevent players from using certain other abilities during their effect, such as to prevent players from combining excessively powerful buffs. Similarly, Divine Shield, Lay on Hands and Hand of Protection use the forbearance debuff to prevent a player from receiving any of these effects within 1 minute of each other. However, they do not share a cooldown, and so can be used in short succession on three different targets.

Global cooldown
The global or universal cooldown, frequently shortened to "GCD", is the cooldown which starts every time you start to use a spell or ability, and affects all of your class spells and abilities. There are exceptions to this, however, as noted below.

The term 'global' is also often used to refer to a single global cooldown. In this way it serves as a basic unit of measurement for time and ability usage. It may take a certain number of globals to set up a rotation, to deal a certain amount of damage/healing, or to respond to an event. The phrase 'to global' (or 'to be globaled') refers to being killed extremely quickly, such as in the duration of only a single GCD.

If a spell has a casting time less than the global cooldown (or instant cast), you generally have to wait the remainder of the global cooldown. If a spell with casting time is interrupted before it has finished casting, the global cooldown is canceled. This allows you to immediately begin casting a new spell, be it the same spell or another.

The base global cooldown is generally 1.5 seconds for all classes except rogues, Cat Form druids, and monks, whose abilities mostly have one second global cooldowns. However, since patch 2.4.0, haste can reduce the global cooldown to a minimum of 0.75 seconds (1.0 seconds prior to Legion) for the spells that originated from 1.5 second cooldown. Haste doesn't affect GCD of agility energy melee classes like the ones mentioned before. A few specific abilities have global cooldowns as short as 0.5 seconds. The global cooldown affects the wait for the next ability, so using an item or ability with the standard 1.5 second cooldown will require waiting that long before a 1 second global cooldown ability can be used.

Some abilities are not affected by the global cooldown, and do not trigger the global cooldown when used. This means that they can be used at times when other abilities cannot (such as immediately after using an instant ability), and can be followed immediately by another ability without delay. Such abilities are often referred to as being "off the global cooldown" or "not affected by the GCD". All such abilities are currently instant cast, allowing several to be used simultaneously, followed immediately by the use of another ability. Many of these abilities have the effect of augmenting the character in some way, and are often placed in macros with other abilities, for speed and convenience.

As of Battle for Azeroth, a significant number of abilities which previously were not on the global cooldown have been added to it. Notably, the majority of DPS and healing cooldowns and movement abilities have been added to the global cooldown. Some but not all defensive abilities have also been added to the global cooldown.

Abilities noted for not affecting nor being affected by the global cooldown:

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 * Death knight
 * Anti-Magic Shell
 * Blood Tap
 * Dark Command
 * Death Grip
 * Empower Rune Weapon
 * Hysteria
 * Icebound Fortitude
 * Lichborne
 * Mind Freeze
 * Rune Tap
 * Vampiric Blood
 * Bone Shield
 * Symbiosis: Might of Ursoc (Symbiosis)
 * Druid
 * Maul
 * Nature's Swiftness
 * Barkskin
 * Frenzied Regeneration
 * Survival Instincts
 * Nature's Grasp
 * Hunter
 * All Aspects (1 second shared cooldown)
 * Deterrence
 * Kill Command
 * Silencing Shot
 * Symbiosis: Dash (Symbiosis)
 * Mage
 * Arcane Power
 * Blazing Speed (can also be cast while a cast time spell is in progress)
 * Cold Snap
 * Combustion
 * Counterspell
 * Ice Floes (can also be cast while a cast time spell is in progress)
 * Icy Veins
 * Presence of Mind
 * Temporal Shield
 * Monk
 * Avert Harm
 * Chi Brew
 * Chi Torpedo
 * Clash
 * Dampen Harm
 * Diffuse Magic
 * Elusive Brew
 * Energizing Brew
 * Fortifying Brew
 * Guard (monk ability)
 * Invoke Xuen, the White Tiger
 * Provoke
 * Purifying Brew
 * Roll (monk ability)
 * Spear Hand Strike
 * Thunder Focus Tea
 * Tigereye Brew
 * Zen Meditation
 * Symbiosis: Survival Instincts (Symbiosis)
 * Paladin
 * Ardent Defender
 * Avenging Wrath
 * Devotion Aura
 * Divine Protection
 * Guardian of Ancient Kings
 * Holy Avenger
 * Lay on Hands
 * Rebuke
 * Reckoning
 * Righteous Fury
 * Shield of the Righteous
 * Speed of Light
 * Protection Spec Guarded by the Light: Word of Glory
 * Protection Spec Symbiosis: Barkskin (Symbiosis)
 * Priest
 * Archangel
 * All Chakras (30-second shared cooldown)
 * Desperate Prayer
 * Fade
 * Guardian Spirit
 * Inner Focus
 * Leap of Faith
 * Pain Suppression
 * Power Infusion
 * Power Word: Barrier
 * Silence
 * Spirit Shell
 * Vampiric Embrace
 * Void Shift
 * Rogue
 * Cold Blood
 * Preparation
 * Evasion
 * Sprint
 * Vanish
 * Kick
 * Symbiosis: Growl (Symbiosis)
 * Shaman
 * Ancestral Swiftness
 * Elemental Mastery
 * Shamanistic Rage
 * Wind Shear
 * Symbiosis: Solar Beam (Symbiosis)
 * Symbiosis: Prowl (Symbiosis)
 * Warlock
 * Soulburn
 * Warrior
 * All warrior stances (1.5-sec shared cooldown)
 * Avatar (warrior ability)
 * Charge
 * Cleave
 * Deadly Calm
 * Hamstring
 * Heroic Strike
 * Inner Rage
 * Intervene
 * Pummel
 * Recklessness
 * Shield Barrier
 * Shield Block
 * Shield Wall
 * Sweeping Strikes
 * Symbiosis: Savage Defense (Symbiosis)

Racials
 * Blood elf
 * Arcane Torrent
 * Draenei
 * Gift of the Naaru
 * Orc
 * Blood Fury
 * Troll
 * Berserking

Abilities that are affected by but will not themselves trigger the global cooldown:
 * Tauren's War Stomp
 * Paladin's Avenging Wrath

Abilities with irregular global cooldowns:
 * Warlock's Shadowfury: Triggers a 0.5 second global cooldown.

Cooldown and usage theory
The cooldown determines how often something (spell, ability, or item) may be used. Specifically, it has an inverse relationship to how many times per fight it may be used.

Here's a rough guide to help with when to burn a cooldown:

Item cooldowns
Items with cooldowns are simply items that have limit on how often you can use them.

For example Major Healing Potion has a 2 minute cooldown, so it can be used just once every 2 minutes. The average cooldown is 2 or 5 minutes, but they range from 10 seconds to 3 hours (like Signet of Expertise) to 3 days at the longest. These items can be equipped in a variety of slots or used from the backpack.

Most consumable items have a shared cooldown, such as alcoholic beverages.

These items have a long cooldown (this isn't an exhaustive list):
 * Snowmaster 9000 (1 day)
 * Elune's Lantern (1 day)
 * Mr. Pinchy (2 days; 3 charges)

Most equippable items with "Use" effects have a 0 second global cooldown.

Internal cooldowns
An internal cooldown is the cooldown on several abilities usually found on items. It exists as a regulator to prevent specific chance-to-proc abilities from being active at all times. One example is Pendulum of Telluric Currents which has a 10% chance to proc and a 45 internal cooldown. When it does proc, there will be 45 seconds before it can do so again. Internal cooldowns vary in duration, but the most common is 45 seconds as with the Pendulum of Telluric Currents.

Internal cooldowns are often hard to perceive and measure. This is because the description of the item which holds the ability rarely tells if there is any cooldown on the ability, nor how long any possible cooldown is. As a result, internal cooldowns are often mentioned as "hidden cooldowns". Because of this, the cooldown of an item's ability is usually discovered via player testing in-game. It is important to know the internal cooldown of an item's ability since it highly affects how powerful the item is. One example is Darkmoon Card: Greatness. It has a 35% chance to proc, a 15 second duration and a 45 second internal cooldown. If there were no cooldown, players would be able to refresh the duration via procs over and over, enjoying a nearly permanent effect from this item. Applying the cooldown will reduce the time the effect is active to 33% possible uptime (as 15 is 33% of 45), which in comparison reduces the item's performance by almost 70%.

Tradeskill cooldowns
Several professions have recipes with long cooldowns. Note that many "1 day" cooldowns do not in fact last 24 hours; rather they have a daily reset time (usually 1am server time) at which point the cooldown is reset.
 * Alchemy has several transmutes with cooldowns. Many older transmutations have a shared 20 hour cooldown, while Transmute: Living Elements and Transmute: Living Steel each have a 1-day cooldown. Northrend Alchemy Research has a 3 day cooldown.
 * Enchanting has a 2 day cooldown for Void Sphere.
 * Inscription has separate 20 hour cooldowns for Minor Inscription Research and Northrend Inscription Research.
 * Jewelcrafting has two separate 20 hour transmutes for Icy Prism and Brilliant Glass.
 * Mining had a 20 hour cooldown for Titansteel Bar. This was removed with patch 3.3.3.
 * Tailoring has separate 7 day cooldowns for each recipe (except Dream of Destruction) of Dreamcloth.