Orb in off hand.
Orbs are Wizard-specific items found in Diablo III. Orbs are equipped in the off hand, like shields, but they do not have defensive bonuses and can not be used to block with. They look like crystal balls, and function as items with bonus stats to offense and spell-casting abilities. Using an orb is essentially a way for a Wizard to dual-wield caster weapons, at the cost of whatever defensive bonuses she might have obtained from using a shield.
Little is yet known about orb stats or properties. In theory, it seems like every Wizard would want to use one, since a wand or dagger + and orb would surely grant more offensive bonuses than just a single weapon, such as a two-handed staff. There must be some penalties to that equipment choice though, to balance things out.
Orb Visuals
The Wizard is seen holding an orb in her cinematic introduction movie and orbs can also be discerned in several in-game screenshots. A few sample images are below.
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File:Orb-wiz1.jpg|A Wizard casts a spell with a wand in her right hand and an orb in her left.
File:Orb-wiz2.jpg|A dropped orb gleams in the lower right corner of this action shot.
File:Orb-wiz3.jpg|Wizard with orb and Leoric's ghost.
File:Orb-wiz4.jpg|Wizard sees her reflection and Leoric in this orb.
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