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An account bound item in Diablo III.

Bind on Account, or BoA for short, is a way of describing an item that cannot be traded to other players. The item can still be transferred among characters on the same account. This is implemented in Diablo III.

All gold is account bound, as are all crafting materials (except Exquisite EssenceIridescent Tear, and Fiery Brimstone) , quest items, and marquise and higher gems. Gems below marquise can still be traded.

All legendary and set items dropped since patch 2.0 are account bound, to an extent. The item will be tradeable for the next two hours of gameplay to any player that was in the same game when the item was dropped. After two hours of gameplay, the item will be permanently bound to the account in possession of it. Crafted legendary and set items are account bound as soon as they are crafted, regardless of the presence of other players.

Items of any quality weaker than Legendary/Set items will only become Account-Bound if they are enchanted, socketed with Account-Bound gems or otherwise modified.