A prophet was someone who spoke or wrote prophecies.
In 2367, the impostor masquerading as Ardra told Acost Jared and the other Ventaxians not to "talk like some ancient prophet around me, with thees and thous and most powerful ones". (TNG: "Devil's Due")
In 2377, upon The Doctor's expression of disinterest in being worshipped by other holograms as the central focus of a new religion, Iden told him, "Prophets are chosen, Doctor. It's a blessing and a burden." (VOY: "Flesh and Blood")