In Destiny, the floating robotic companion that revives Guardians is called a Ghost.
Ghosts are small artificial-intelligence entities associated with the Traveler. They search for people capable of wielding the Light, resurrect them after death, and help them function as Guardians. In the original game's opening, the player's Ghost finds the remains of a long-dead person in Old Russia and brings that character back to life.
A Ghost is more than a guide or scanner: it can provide navigation, analyze technology, open systems, heal its Guardian, and perform resurrection. The player's Ghost is generally referred to simply as “Ghost,” while some other Ghosts in the wider Destiny universe have individual names.
The answer is easy to confuse with a Servitor, which is a Fallen machine used for worship and resource distribution, or a Sparrow, which is a fast personal vehicle. A Frame is another kind of artificial construct, but it is not the Guardian-reviving companion.