Psychics, unlike magic users, don't rely on external sources to use their powers, but derive the abilities from a unique connection with psionic energy within themselves. They channel this energy (either knowingly or unknowingly) to manifest different abilities such as telekinesis, pyrokinesis, astral projection, mental domination, mind-reading, telepathy, and a slew of others that vary from person to person.
Role of Psychics
On land, those with psychic abilities are regarded with distrust and skepticism. A skilled cleric might pass psychic powers off as messages from their god, but for the most part how psionics work isn't really known--or trusted. There is also a link between psychic powers and mental instability, which may be why most believe they are lunatics anyway.
Merpeople, on the other hand, make use of their most powerful psions as oracles, who rule the rest of the people. These exceptional women are the voice of the deep for their fellow followers, and guide them in their eternal struggle against the world's dangers.