The consciousness transfer is a Na'vi ritual where a consciousness of a single being is transferred from one body to another.
The goal is to transfer the spirit or consciousness of the individual that it is being practiced upon into a "comatose" or empty body permanently by passing them through the "Eye of Eywa." It is done by joining an entire clan's queues into one of the neural link locations on Pandora (e.g. the Tree of Souls) and performing a Terran equivalent of a large-scale ritual chant presided over by the Tsahìk. It is, by all means, a risky endeavor in that if the subject is very weak, it can result in death.
It has only been known to happen on two occasions, both performed at the Tree of Souls, where the body into which the transfer was being attempted was an avatar. The first was on Dr. Grace Augustine, when suggested by Mo'at, the Tsahìk of the Omaticaya clan. Dr Augustine did not survive due to previously sustained life-threatening wounds. However, it is suggested that her consciousness does still exist within Pandora's neural network and was not destroyed. The second was on Jake Sully who, because he was relatively healthy at the time of the ritual, survived and his consciousness was moved permanently in his avatar body.
In Avatar: The GameEdit
The consciousness transfer also occurs in James Cameron's Avatar: The Game with Able Ryder, who survives the transfer and Dr. René Harper who succumbs to his wounds during the ritual. This event only happens when playing for the Na'vi faction.