Psychic Resevoir: The term given to a field of energy that surrounds all inhabited planets. Psychic resevoirs are created by the ongoing thought patterns of living beings; more complex beings give off significantly more energy than less complex ones.
A psychic resevoir requires a certain degree of consciousness in order to form. With very few exceptions, bacteria and plants lack the self-awareness required to produce or be affected by telepathic waves, and thus fail to create any psychic energy to be added to resevoirs. Animals produce minute amounts, while sentient beings tend to produce psychic energy in massive waves. On Earth, for example, the combined product of hundreds of millions of years of animals is believed to have been approximately equal to the amount of psychic energy that the Earth's current population could produce in one thousand years.
Once produced, psychic energy is drawn into orbit around the planet that produces it. It does not seem to fade or degrade under normal circumstances; instead, it simply continues to gather until the planet's orbit is completely suffused with energy; this fills the 'resevoir' of the planet, at which point further energy produced spirals into space.
Many scholars believe that psychic resevoirs may be at least partially responsible for the development of sentience and for early development of psychic powers; they theorize a sympathetic reaction to the thought-patterns filling the air around beings. This is difficult to judge precisely; all known civilizations spent the bulk of their psychic resevoirs early in their existance - some consider this to be a form of circumstantial proof.
Tapping the Resevoir
Most telepaths are capable of accessing other minds by passing through the psychic resevoirs on a planet; tests have shown that psychics are much less powerful if forced to use their capabilities in space, or on planets that never supported life. Accessing a resevoir allows a psychic to avoid drawing on their own stores of power, which in turn lets them use their abilities longer and more effectively than usual. And since psychic energy is continually replenished by local populations, it is considered to be a renewable resource with few downsides.
The nature of this resource has led several civilizations throughout documented galactic history to use psychic energy as a foundation for Pseudotech; for reasons that are unclear, the psychic fields resist proper documentation by standard technology. On Earth, the most famous such civilization was Atlantis, which devoured so much psychic energy over its history that it completely tapped out Earth's supplies, rendering the making of further Atlantian technology on Earth impossible. Even more dramatic were the Chitrani, who managed to wipe out their entire species by over-relying on psychic energy, and then attempting to raid and destroy other planets in order to make up the difference. Less dramatic were the Adar Theocracy of the Sayleen, who gradually siphoned power over the course of several thousand years to build their empire, or the Yaughud of the Trox, who succeeded in controlling every psychic with access to their resevoir for centuries, restricting use to emergencies when the resevoir originally ran low.
Earth's psychic resevoir remains low, but the large human population ensures that there is always at least a low-level amount of energy for human psychics to draw off of. Considering the resource to be free and renewable, human governments have yet to apply any laws to use of the resevoir, beyond restricting new technologies that require it to function.