In Assassin's Creed, the Animus lets modern characters experience ancestral memories.
The Animus is a fictional machine that reads genetic memories preserved in a person's DNA. It allows a modern user to relive events experienced by an ancestor, rather than physically traveling into the past. This device provides the series with its central structure: historical gameplay is presented through a modern framework.
Desmond Miles is the first major modern-day user shown in the series. Abstergo Industries forces him to use the Animus so researchers can investigate the memories of his ancestor Altaïr Ibn-La'Ahad. Later games introduce different Animus users, modified versions, and technologies that can record or simulate memories.
The Animus is not the same as a Piece of Eden. Pieces of Eden are ancient Isu artifacts with extraordinary technological abilities, while the Animus is a modern machine designed to access genetic memory. The series also uses Animus glitches and synchronization limits as explanations for gameplay boundaries and visual effects.