Clairvoyance originally meant seeing over a distance i.e. seeing something happening on the other side of the world, but now is the general term for mediumship for passing on information gained through a spiritual link.
Clairvoyants can also see into the future, and these ‘prophecies’ become strong evidence of the spiritual link when they come about, even if it is something trivial.
Clairvoyance is the generic term for linking with a spirit guide and passing on a message from a person who has passed with the intention of proving life after death. Strictly speaking clairvoyance is seeing, clairaudience is hearing, and clairsentience is feeling, but that should be transparent to the customer. The best proof is predicting the future, or giving information that the customer does not know of, and has to check with someone else if it matches the person who has passed, which proves it is not mind reading. Most mediums will also use psychic skills, particularly when warming up, or if on a weak spiritual link, which basically is mind reading. Psychometry can also be used, where the customer brings an object, and the reading is about whatever has been around that object during its existence, i.e. a ring, etc.
Other props can be used for ‘scrying’ such as sand imprint readings, water readings, crystal ball, and other associated props such as Tarot/Palms/etc.
The term medium means that he is the link between the customer and spirit and nothing passes through either way without him as the filter for safety. So don’t try this at home kids (i.e. do not use a Ouji board without a trained medium present). The medium cannot get information on request, and can only pass through what is there when he tunes in, i.e. it is like watching TV, so if you are looking for a particular person if he is not on one of the channels you will have to take the message from whoever comes though
that knows you and try another time. Any medium who guarantees a link with a particular person in spirit is a fraud.
The medium can also read the aura of a person, but this is used for training rather than being of use generally because, if he is a healer, he can sense any problems with the aura (caused by the body underneath that area) during a healing session.