"Physical: A myriad of skills that harm enemies in conventional ways, such as the Barbarian’s Bash or the Demon Hunter’s Impale, are classified as Physical. As you grow in power, several of your Physical abilities will gain new runes that change their damage type while providing added effects. Abilities and runes that don’t actively deal damage (such as the Crusader’s Laws of Justice and its variations) are also classified as Physical, but their effects are not increased by added Physical damage on your equipment.

Fire: Skills that deal Fire damage typically offer up unrivaled offense at the cost of utility. Massive offensive bonuses, additional damage over time, and increased resource generation fuel the searing destruction of your enemies.
Cold: Many Cold damage skills slow or freeze your enemies; others leave them vulnerable to additional damage while they are chilled or frozen.

Lightning: The Lightning damage variants of some abilities can stun targets, increase the number of enemies affected, or reduce resource costs and cooldowns for greater efficiency in combat.

Poison: Vile afflictions dealt by Poison type abilities weaken enemies, damaging them over time and reducing their effectiveness in combat. Many of the Witch Doctor’s offensive skills fall under this damage type.

Arcane: Abilities that rapidly disintegrate enemies with raw magical power and elemental forces of nature fit this damage type. Several of the Wizard’s offensive skills deal Arcane damage.

Holy: On top of dealing damage, the offensive powers of holy magic employed in battle by Crusaders and Monks can disrupt enemy behavior or provide defensive bonuses."