Holy Damage

Holy is one of the types of damage in Diablo III. It is white in appearance.

Holy damage is not well known, and has thus far been seen only on a few Monk skills; Circle of Wrath, Lethal Decoy, Retribution Aura, and Wave of Light. Runestones might add it to other spells in the game, or it may be found as an item modifier, though this one seems like it might be Monk-only.

It's not known if any monsters deal Holy damage, but it seems unlikely.

It's not known if Holy damage can be resisted, but it can presumably be reduced or absorbed. It can not be blocked.

Critical hits scored with Holy damage provide an unknown bonus. It's possible that Holy damage deals extra damage to the Undead.

Diablo III Damage Types

Blizzard's @Diablo Twitter feed added some clarification about damage types in posts made in early December 2010.[1]

any change in the range of damage types to include holy, shadow, voodoo or anything else to match the classes? —Scyberdragon

Damage types will likely change some but are currently Physical, Fire, Lightning, Cold, Poison, Disease, Arcane, and Holy. —Diablo

Whats the difference between poison and disease damage?—WickedBubba
Disease has a damage debuff (both intake and output), and poison has a health debuff (regen/heal). Subject to change of course.—Diablo

Is there much difference between poison and disease? They’re both internal maladies that hurt over a period of time.—Grug

Fairly significant in their difference, but both countered with a single resistance. Damage/resists aren’t design complete though.—Diablo