Potential energy

Potential energy was the energy from the possible futures of an individual and possibly other entities.

The Weeping Angels fed on potential energy, though some used other sources. (DW: The Time of Angels/Flesh and Stone) A Weeping Angel would touch someone, sending them to the past while feeding on the lives they might have had. This led the Tenth Doctor to describe them as "the only psychopaths in the universe to kill you nicely," since their method of killing was to let their victims "live to death". (DW: Blink)

The Oroborus also seemed to feed off potential energy, though not as "nicely" as the Weeping Angels, as it turned the planet Centauri into a black hole by "siphoning off its future", as Alistair Gryffen said. (K9TV: Oroborus)