Mediumship is the practice of purportedly mediating communication between spirits of the dead and living human beings.  Practitioners are known as "mediums." There are different types of mediumship, including spirit channeling 

Spiritualists classify types of mediumship into two main categories:

 "mental" and "physical":

• Mental mediums purportedly "tune in" to the spirit world by listening, sensing, or seeing spirits or symbols.
• Physical mediums are believed to produce materialization of spirits, apports of objects, and other effects such as knocking, rapping, bell-ringing, etc. 

 "Mental mediumship" is communication of spirits with a medium by telepathy.  The medium mentally "hears" (clairaudience), "sees" (clairvoyance),  and/or feels (clairsentience) messages from spirits. Directly or with  the help of a spirit guide, the medium passes the information on to the  message's recipient(s). When a medium is doing a "reading" for a  particular person, that person is known as the "sitter".  

 "Trance mediumship" is often seen as a form of mental mediumship. Most  trance mediums remain conscious during a communication period, wherein a  spirit uses the medium's mind to communicate. The spirit or spirits  using the medium's mind influences the mind with the thoughts being  conveyed. The medium allows the ego to step aside for the message to be delivered.  

 Physical mediumship is defined as manipulation of energies and energy  systems by spirits. This type of mediumship is claimed to involve  perceptible manifestations, such as loud raps and noises, voices,  materialized objects, apports, materialized spirit bodies, or body parts  such as hands, legs and feet. The medium is used as a source of power  for such spirit manifestations.  

 In the later half of the 20th century, Western mediumship developed in two different ways. One type involved clairaudience or sensitives who hear spirit, and then relay what they hear to their clients.The other incarnation of non-physical mediumship is a form of  channeling in which the channeler goes into a trance, or "leaves their  body", allowing a spirit entity to borrow their body, who then speaks  through them. When in a trance the medium appears to come under the control of the spirit of a departed soul, sometimes entering into a cataleptic state,although modern channelers may not.[citation needed] Some channelers open the eyes when channeling, and remain able to walk  and behave normally. The rhythm and the intonation of the voice may also  change completely.