The Apple of Eden is the ancient artifact sought by Abstergo in the original Assassin's Creed.
In the game's story, Abstergo uses Desmond Miles to relive Altaïr Ibn-La'Ahad's memories because Altaïr encountered one of the mysterious Pieces of Eden. The Apple is portrayed as a powerful Isu artifact capable of influencing human perception and behavior.
Pieces of Eden are recurring objects in Assassin's Creed fiction. They connect the historical plots to the ancient civilization that existed before recorded human history in the series' mythology.
The name can be confused with other Eden artifacts. The Sword of Eden and the Shroud of Eden are separate Pieces of Eden appearing elsewhere in the franchise. The original game's target is specifically the Apple recovered during Altaïr's missions.