In Assassin's Creed, the Animus is the machine that lets users relive ancestral memories.
The device is a fictional technology central to the series' framing story. It reads genetic memories inherited from ancestors and presents them as interactive experiences, allowing a modern user to explore historical periods without physically traveling through time.
Desmond Miles is connected to an Animus in the first game by the modern-day Templar-controlled company Abstergo. His ancestor Altaïr's memories provide the main historical setting. Later games show different Animus models, portable versions, and systems used by Abstergo and its rivals.
The Animus is not the same thing as Eagle Vision, which is an Assassin-related perception ability used inside the historical simulations. “Helix” is another virtual-memory product associated with the franchise, especially Assassin's Creed Unity, but the classic machine itself is called the Animus.