According to Assassin's Creed lore, the Animus lets modern characters relive the memories of their ancestors.
The Animus is a fictional machine that reads genetic memories and presents them as an interactive simulation. Desmond Miles uses it in the early games to experience the lives of ancestors such as Altaïr Ibn-La'Ahad, Ezio Auditore, and Connor. Later stories introduce other users and versions of the technology.
The device provides the series with its central storytelling structure: a modern character can investigate the past without physically traveling through time. The historical sections are therefore framed as reconstructed memories, which allows the games to combine real events with fictional characters and conspiracies.
The Apple of Eden is a different Isu artifact, while the Bleeding Effect describes a consequence of repeated Animus exposure. Neither is the machine itself. The Animus is also not a conventional historical device; it belongs to the series’ science-fiction framework involving genetic memory and the precursor civilization known as the Isu.