The Animus is the fictional machine that accesses genetic memories in Assassin's Creed.
In the series' modern-day framing story, people enter the Animus to experience memories inherited through their genetic lineage. Desmond Miles is the first major user shown in the games, and the machine lets him relive the lives of ancestors such as Altaïr Ibn-La'Ahad and Ezio Auditore.
The Animus provides the narrative explanation for moving between historical periods while keeping a modern storyline active. It also explains why a player can explore reconstructed historical environments through a contemporary character's experience.
The term is sometimes confused with Helix, which is a later entertainment and research platform within the fictional universe. Eagle Vision is an Assassin ability for identifying people and objects, while the Observatory is a location and surveillance device in Assassin's Creed IV: Black Flag. Neither is the machine used to access genetic memories.