The device used by Desmond Miles in the first Assassin's Creed games is called the Animus.
The Animus is a machine that lets a user access genetic memories inherited from ancestors. In the early games, the Abstergo Industries scientist Warren Vidic operates the device while Desmond is forced to relive the memories of Altaïr and later Ezio. These historical sequences form the main gameplay worlds, while Desmond's modern-day scenes provide the series' continuing framework.
The technology does not literally send a person into the past. Instead, it reconstructs ancestral memories from genetic information and presents them as an interactive experience. Later versions and related devices appear throughout the franchise, with different groups adapting the technology for their own purposes.
The Bleeding Effect is a consequence of prolonged Animus exposure, not the machine's name. It describes the user's acquisition of skills or personality traits associated with an ancestor, which is why the terms are often mistakenly treated as synonyms.