channeling is the process of communicating with spirits who are not currently inhabiting bodies. More specifically, the communication is based in either telepathic or direct spirit-to-body contact (or both).  You can think of telepathy as a more refined and subtle form of verbal communication. Spirit-to-body contact can and often does involve some amount of "taking over" of the channeler's body. In extreme cases, this can become possession, either with conscious agreement from the channeler or not.  Last century, when spiritualism took root in Western Europe and the United States, channelers were called mediums. Before that, they might have been said to "hear voices" (such as with Joan of Arc) or to be prophets, such as with Muhammad, Jesus, and many of the other well-known Middle Eastern mystics. The oracles at Delphi were almost undoubtedly channelers, as were many others in the service of a wide variety of deities throughout time and history. Channeling has come to mean communicating with entities who have either inhabited a body but now don't or who claim to have never inhabited a body. It is possible to channel someone who is currently inhabiting a body, though that isn't generally what people mean when they speak of channeling. For completeness, though, do bear in mind that the definition includes this aspect.