rage, energy, and mana (wow)  

Every character has a resource that is needed to perform most abilities. For most classes, this is mana, and some players will simply refer to all these resources as mana. However, rogues use energy and warriors build rage which use slightly different mechanics. The only thing energy and rage have in common with mana is that they are needed to perform abilities.

Mana

All classes except rogues and warriors use mana. While some often refer to all these classes as "casters," it's difficult to refer to a hunter as a caster. ^[1] However, because there are so many classes that use mana, there are many effects in the game that deal specifically with mana, either increasing the regeneration of it or burning it away, for example.

The amount of mana a character has grows significantly as they level, just as their health does. The total amount of mana a player can have is called their mana pool. 1 point of intellect will increase the mana pool by 15. When a mana-user casts a spell, they will use up some number of mana, and if it is not available, they cannot cast the spell. Because higher ranks of an ability have a stronger effect, they also consume more mana. Using mana wisely is important since it is difficult to regain, at least while in combat.

Mana Regeneration allows a player to recover some mana as time goes on. A players natural mana regeneration is tied to the character's spirit, however any time an ability is used that consumes mana, it triggers the "5 second rule" that prevents any regeneration for the next 5 seconds. Thus, if a player is casting spell after spell without pause, they will probably regenerate no mana during this time period. However, the attribute "mana per 5 seconds" (or MP5,) will continue to operate. Although MP5 tends not to be quite as strong, it is considered vital by many casters at higher levels.

The other means of regaining mana is through drinking. However, this can only be done out of combat.

Energy

Rogues have a much simpler system. They start with 100 energy. When they use an ability, it takes a chunk out of the energy bar, and every 2 seconds they get 20 points back. Rogues never have more than 100 energy (except for the talent Vigor,) but the energy cost of their abilities does not increase with rank. This means that while a rogue cannot constantly use abilities for very long compared to a caster, they will also be able to continue to frequently use abilities until the battle ends.

Many rogues form complex systems of how they open their battles to use their initial 100 points of energy in the most optimal manner possible. Some of their talents reduce energy costs to make this more effective.

Druids in cat form behave like a rogue and also use Energy. Most of their abilities are very similiar to some rogue skill. Additionally, hunter pets have an attribute called Focus that behaves identically to energy.

Rage

The warrior's rage behaves very differently. While it is still spent on the use of abilities, the means of gaining rage are unique.

By default, energy and mana tend to fill up when not being used. Rage, on the other hand, gradually depletes when it isn't being used, and warriors often begin a battle with no rage whatsoever. However, every time a warrior attacks or is attacked, they gain a few points of rage, to a maximum of 100.

Warriors also have a few abilities that add to rage. Charge will add up to 15 rage when used to begin a battle, and Bloodrage also grants the warrior several points of rage, and can be used out of combat. Unused rage will remain in the warrior's pool until it is used or combat ends. At the end of combat, rage gradually dwindles.

One additional side effect of rage is that it is nearly or entirely lost when changing stances. While most battles will be fought in a particular stance, this makes it prohibitive to, for example, switch from defensive stance to fury to intercept a target that has run away, and then move back into defensive.

A large number of warrior talents affect the generation or use of rage in some way.

Druids in bear form also use Rage.

See Rage Generation.

1. ^ Hunters were originally intended to have their own unique resource as well, called Focus, but Blizzard decided that the specifics of focus were anti-thematic to the class. Now Focus is the name of the hunter pet's energy.