The Animus is the device that lets modern characters experience the genetic memories of their ancestors in Assassin's Creed. It is presented as a machine that interprets inherited memories and recreates them as interactive historical simulations.
Desmond Miles is placed in an Animus by Abstergo Industries in the first game. His sessions allow players to experience Altaïr's life while also revealing a modern conflict between the Templars and the Assassins. Later games introduce different versions and interfaces, including portable and virtual-reality systems.
The Animus is not the same as an Apple of Eden, which is an ancient Piece of Eden, or Eagle Vision, which is a perception ability used by several characters. The Bleeding Effect is a side effect of repeated Animus exposure, not the machine itself.