Every ability, power, or spell belongs to one of seven magic schools which define what can be done to absorb, immunize against, or resist it. Your resistance against five of these schools was displayed in your character information, but resistance as a game mechanic was removed with Mists of Pandaria.
If you are a caster, and an opponent uses , , , , , , or on you while you're casting a spell, these and other abilities will not only interrupt that spell but also to prevent you from casting any spell in that school for some amount of time. It's good to know what schools your abilities are in so you can switch to another when this happens. It's fairly clear for Mages (the school of the spell is the same as the tree it falls under) and Warlocks (if it doesn't involve fire, it's Shadow). For other classes it's not always clear. Fortunately, the tooltip of any damage spell will specify the type of damage it does. Warriors are the only class that strictly deals only one damage type, that being Physical. Hunters and Shamans have the most varied damage types, with both being able to deal Physical, Nature and Fire damage, as well as Arcane and Shadow for Hunters and Frost for Shaman.
Not presented as magic to the user, but treated as a school by the game mechanics. All classes use physical type damage, as attacking with a weapon falls into this school; the target can use Defense to avoid the attack, a shield to it, the skill to block it with a weapon, and Armor to resist some of the damage if all else fails. Damage taken is physical damage. Most Warrior, Rogue, and Monk abilities are Physical. Death Knight abilities obtained by spending talent points in the Blood Tree do physical damage. The Armor penetration skill also only ever applies to physical damage dealt.
Some physical abilities, like and , are treated like spells. These abilities have a chance to miss like all spells, which can be offset by Hit rating, but resistance to these abilities cannot be increased.
Most non-damaging magical hunter abilities, including Silencing Shot, Hunter's Mark, Misdirection, and Distracting Shot are Arcane-based. Arcane Shot, however, is a main source of direct damage, as is the druids' Moonfire and Starfire. Also, the blood elf racial ability Arcane Torrent is Arcane-based. (Before patch 3.0.2, night elf priests could do Arcane damage with Starshards.)
The true masters of the Arcane, however, are mages. For mages, the Arcane school is primarily a utility line rather than a damage line. Any spell from a mage's Arcane ability category is of the Arcane school, including four spells that do damage (Arcane Missiles, Arcane Explosion, Arcane Blast, Arcane Barrage) and a very broad range of utility spells: Polymorphs, Arcane Intellect, Mana Shield, Mage Armor, Blink, Teleports, Portals, Counterspell, and Conjure Mana Gems, Food, and Water.
Hostile Arcane spells (including those that do no damage) can be resisted; there are items that increase one's Arcane resistance. Arcane is the only resistible magic school against which players cannot increase their Resistance via class abilities, short of abilities which increase all Resistances like Mark of the Wild.
Spells of the Fire school typically inflict damage, which can be direct damage and/or damage over time. Mages and Warlocks use it as one of their primary sources of damage, while Shamans, Hunter traps, and engineers also use the Fire school.
Many spells and environmental effects (such as lava) do Fire damage. The class most associated with the ability to control fire is also the Mage. Fire is also one of the fundamental elements that Shamans can manipulate with their Totems. To a lesser extent, Warlocks can also deliver Fire damage. Warlocks specced heavily into their Destruction talent tree are sometimes called "Firelocks". Hunters' Immolation Trap, Explosive Trap and Explosive Shot also deal Fire damage; similarly, explosives and damaging trinkets created by Engineers typically do Fire damage. Mages can absorb Fire damage with Fire Ward.
Like Arcane resistance, Fire resistance is a statistic that can be affected by spells and items. Paladins and Shaman can specifically increase Fire Resistance with Fire Resistance Aura and Fire Resistance Totem respectively. A Warlock's Imp can cast Fire Shield to increase fire resistance of friendly player characters and pets, but only the highest rank (Rank 6) will do so.
The Frost school is effective both for attack (doing damage) and defense (raising armor value). Frost spells often inflict snare or root effects, as well. Mages, Shaman, Death Knights and the occasional Hunter trap uses the Frost school.
Mages and Death Knights have Frost talent trees, and obviously any spell in those trees is of the Frost school. Of course, Shamans' Frost Shock is of the Frost school too, as well as the Hunter's Freezing Trap, Freezing Arrow and Frost Trap. Water-based abilites used by bosses also fall under the frost category; for instance, Rokmar the Crackler's Water Spit. Mages can absorb Frost damage with Frost Ward.
The Nature school is usually used for nature based attacks, buffs, and curative spells. Nature damage can be direct damage (like lightning) or damage over time (like poison). This means that Rogues (poison), Shamans, Druids, Monks, and Hunters (stings) have access to Nature damage.
Acids, diseases, and poisons inflict Nature damage, and damage from lightning is also considered part of the Nature school. Shamans' and Druids' healing spells are Nature spells, and other nondamaging spells such as Entangling Roots and Faerie Fire are in this school as well. Hunters' Stings and the Snake Trap's viper poisons are Nature based, as are their Mend Pet and Revive Pet abilities. Rogues' poisons are also Nature based.
The opposite of Holy magic, Shadow is probably the most versatile school. Used by Priests, Warlocks, Death Knights and Hunters (Black Arrow) it contains a wide variety of spells. Apart from Direct Damage and Damage over Time spells, there are various utility spells, including Drains, Crowd Control spells, and Debuffs.
Shadow damage is dealt by dark spells such as those of the Priest's Shadow Magic ability category and most of the Warlock's repertoire. The Blood Pact that a Warlock's Imp pet casts to boost the entire party's Stamina is a Shadow effect, as are the creation of a Healthstone or Soulstone and the summoning of demons. Warlocks can also absorb shadow damage with Shadow Ward.
The Holy school is usually related to abilities which heal and aid living beings. There are also a few spells that do Holy damage: Smite and Exorcism, for example. Contrary to popular belief, Holy Magic does not deal additional damage to undead or demons unless specifically mentioned in the tooltip (such as with Exorcism).
It is not possible to resist Holy magic, giving it a slight advantage over other schools, but it does have a basic miss chance like all spells, offset by Hit rating, and spells can be silenced.
Items and Buffs which give a bonus to all resistances, such as Mage Armor, do not include Holy resistance, but percentage-based damage-reduction abilities such as a Warrior's Defensive Stance successfully reduce damage from Holy spells. Also, the , , and items will also absorb limited amounts of Holy damage.
- In the past, a shadow Priest's ability referred to the Priest's Holy talent tree, not the Holy school of magic. Therefore, the priest can still cast holy-based spells from the Discipline talent tree while Shadowformed.