In multi-player video games, particularly MMORPGs, it's common for there to be as many copies of a "quest item" as there are people taking the quest. This trope describes when these quest items should logically be unique within the world. The most extreme case is probably when this is a specific named individual's head (heart, liver, pancreas, whatever); it's also common with bits of a unique magical beast or just items that should be impossible to reproduce, such as a specific lost piece of jewelry or an Artifact of Doom that canonically can't be made anymore.