The Apple of Eden is the Assassin's Creed series' fictional ancient artifact shaped like an apple.
The Apple is one of the Pieces of Eden, powerful devices created by the Isu, an advanced civilization that existed before recorded human history in the series' mythology. It can influence minds, create illusions, and project information, although its exact abilities vary across appearances.
Assassins and Templars repeatedly seek Apples because control of such an artifact could support their competing visions for humanity. Several different Apples appear in the franchise, so the term does not necessarily identify one unique physical object across every era.
The Apple is often confused with other Pieces of Eden, including the Sword, Staff, and Shroud. Those artifacts have different forms and story roles. The apple-shaped device is specifically called an Apple of Eden.