The recurring Precursor artifact called the Apple in Assassin's Creed is the Apple of Eden.
In the series, Apples of Eden are Pieces of Eden created by the ancient Isu, also called the Precursors. They can influence human minds and produce other effects that later cultures interpret as magic, divine power, or miracles.
The artifact appears in several historical storylines, including the first Assassin's Creed game and the adventures of Ezio Auditore. Its power helps explain why Assassins and Templars repeatedly compete to locate and control these objects.
The Apple is not a single ordinary fruit and is not the only Piece of Eden. Other artifacts include the Staff of Eden and the Sword of Eden. The broader term refers to a group of technologically advanced Isu relics rather than one universally unique object.