Psi vampires are people who have a need to feed on the life energy of others in order to maintain a state of good health. Like Sanguinarians (blood vampires), they do not produce a sufficient amount of pranic or "life" energy, and therefore need to replace this energy by feeding on the energy of others.
There are a few different "subtypes" of psi vampires:
Elemental vampires, who feed on elemental energy, such as the energy created during a thunderstorm.
Sexual vampires, who feed on the energy generated by a sex act. (Note: Contrary to popular belief, the succubus and incubus are not sexual vampires. They are in fact a type of demon.)
Emotional vampires, who feed on the emotions of others.