The Animus is the device that lets users view ancestral memories in Assassin’s Creed.
In the series’ modern-day storyline, a person enters the Animus while it reconstructs genetic memories inherited from ancestors. This framing device allows the games to move between a contemporary plot and historical settings without treating the historical sequences as ordinary time travel.
The Animus is central to the stories of Desmond Miles and later modern-day characters. Its technology is fictional, but the games use it to explain why players can experience the lives of many different historical figures. The Animus also supports gameplay ideas such as synchronization, memory sequences, and historical simulations.
The Apple of Eden is a different object: it is one type of powerful Isu artifact, often called a Piece of Eden. The Bleeding Effect is another separate concept, describing memories and abilities that can affect an Animus user after repeated exposure.