Transient Being

The Transient Beings were mentioned by the Fifth Doctor as having the necessary time sensitivity for the operation of the Crystal Bucephalus, along with the Legions, Tharils, Eternals, and Chronovores. (PROSE: The Crystal Bucephalus)

The Sixth Doctor later used "transient beings" when referring to the Great Old Ones. (PROSE: Millennial Rites)