The Animus is the fictional memory-reading machine used in the Assassin's Creed series.
In the modern-day framing story, the Animus allows a person to relive genetic memories inherited from ancestors. Those memories provide the playable historical sequences, including Altaïr's missions during the Crusades, Ezio's adventures in Renaissance Italy, and later protagonists' experiences in other eras.
The device is central to the series' science-fiction premise. It connects the historical settings to the modern conflict between the Assassin Brotherhood and the Templar Order, while also allowing games to explain how a single player can experience many different historical characters.
The Helix is another Abstergo entertainment product and should not be treated as the same device in every context. An Apple of Eden is a powerful precursor artifact, not a memory simulator. Eagle Vision is an Assassin ability that highlights people and objects. Desmond Miles is among the best-known modern users of an Animus.