Psychic energy was a type of energy that powered (or was powered by) mental processes.
Psychic energy had many varied frequencies. One type needed a focus point, a medium to create the energy like a poltergeist and form energy gathering points as a way to coalesque the energy and create psychic projections. It may also have served to connect time zones. (TV: The Awakening)
Both the Nestene Consciousness (TV: Spearhead from Space) and the planet Siralos were made of pure psychic energy. (GAME: Destiny of the Doctors) Silverberg energy was present when there were signs of psychic energy. (PROSE: Alien Bodies)
The destruction of other planets by Zanak liberated energy of many different kinds, including some on the psychic spectrum. This powered the psychic abilities of the Mentiads. K9 Mark II had the power to track mental wavelengths of psychic energy. (TV: The Pirate Planet)
Psychic energy was harnessed like electricity on Hakol and used in combination with technology. The Malus, a war-machine from Hakol, was able to manifest psychic projections that were corporeal enough to interact with their environment. (TV: The Awakening)
Inside the pocket of unreality connected to 19th century Edinburgh by the Spherion-powered Silversmith's Mirrors, the Mirror Image of the Silversmith harvested the psychic energy of dozens of human prisoners to stabilize the bubble dimension in question into a city that mirrored Edinburgh itself. When the human prisoners were freed by the Eighth Doctor and Josie Day, this caused the dimension to collapse. (COMIC: The Silvering)