There are many Stats used by player in the game. They are divided into Primary, and Secondary Stats.
Armor is present on most gear in the game, barring Weapons, Necklaces, and most Rings and Trinkets. Armor reduces damage received by players from non-players.
Stamina directly translates into HP, and is of interest to all classes, as the more HP you have, the longer you can survive when under attack. Tanks need to pay special attention to Stamina.
Intellect directly translates into Mana, and Spell Power, and is of interest to all caster classes, and classes with a healing spec. Mages, Warlocks and Priests primarily use Intellect, as do Balance and Restoration Druids, Elemental and Restoration Shamans, and Holy Paladins.
From Patch 5.0, Intellect will no longer increase the size of the Mana Pool
Spirit is primarily a Healer stat, and is used to increase the Mana regeneration rate, so as to reduce downtime when in Instances. However, Balance Druids, Shadow Priests, and Elemental Shamans can talent for Spirit to also provide them with Hit equivalent to the amount of Spirit. This makes Spirit doubly useful as it will not only increase the rate of Mana regeneration, but will also provide Hit rating.
Attack Power is only seen on some older weapons, and won't normally be seen on newer items. It increases the DPS of your Melee Weapons.
Ranged Attack PowerEdit
This only affects Ranged Weapons, and is of interest only to Hunters. Some enchantments provide this.
This increases the chance that your spells and special abilities have to critically hit your opponent. Critical hits inflict twice the damage, or in the case of healing, heal for double the amount.
This increases your chance to dodge attacks. A dodge is where you avoid the enemy hitting you. Some attacks are undodgeable. Dodge is of particular interest to Druids, as it is their only avoidance stat.
Expertise rating affects the chance that your Melee weapon auto attacks have to be dodged or parried by an opponent. Experise had two caps, a soft cap, and a hard cap. A player who has reached Soft Cap will attack without the monster or boss being unable to dodge it. However, to prevent your opponent from every Parrying your attacks, you need to reach the Hard Cap.
Haste rating affects a variety of things for different players. It decreases the time between Melee weapon auto strikes, it lowers the cast time of spells (Until you reach 1 sec), and it increases the regeneration rate of Runes, Energy and Focus.
Hit rating affects the chance that your special attacks and abilities will miss their target. The cap for melee is 8%, after which, every attack you make will hit the opponent. The spell hit cap for casters is 17%.
Mastery rating can only be taken advantage of by characters Level 80 or higher, and grants individual power enhancement based on the class and spec of the player. See List of Mastery Abilities for more details.
Parry rating affects your chance to parry an opponent's attack. A parry is where you block your opponent's attack, and then make an immediate counter-attack, independent of your own attacks. Parry is of particular interest to Warriors.
From Patch 5.0, Resilience will be granted to players as a base stat, that increases with level. Gear will still grant Resilience, but the gulf between established PvP players and new players will be smaller.
Only normally seen on weapons, Spell Power increases the damage or healing of spells.
Prior to Patch 4.0.1, this reduced the player's chance to be critically hit by bosses. At Level 80, the cap was 540, and was mandatory for Tanks in Raids. Since its removal, all Tank specs are now immune to critical hits from enemies less than 4 levels above them.