Off hand

The off hand, or off-hand, or offhand, is the second weapon slot all characters have access to in Diablo III. While only the Barbarian and Monk can dual-wield weapons, and the Monk is limited to doing so with two fist weapons, all characters can hold some other objects in this slot.

Shields are held in the off hand, in many cases. The Wizard can hold an orb in that hand, teaming it with a wand or a dagger. It's not known if the Witch Doctor will have any off-hand options other than shields.

None of the characters in Diablo III can use two-handed weapons with one hand, so whenever anyone is equipped with one, they do not have the option of an off-hand weapon.