Quest items are items which are either only obtained while a quest is active or are solely useful during a quest and have no useful function when their related quests are inactive. They are not usually possible to trade to other players, but there are some exceptions. Notably, the broken shields received from the Shield of Arrav must be traded with another player in order to complete the quest. Another example of this are the candlesticks received during Hero's Quest.
There are situations where it is not normally possible to obtain multiple copies of the same quest item, such as Excalibur, Garlic, or Khazard chainmail. Most of the time the players may circumvent this by utilising the drop trick.