Clairvoyance is a French word meaning "lucidity". It is an expression of a special sensitivity to the vibrations we humans emit. These vibrations contains information about our emotional life, and can be captured by people with special empathy skills.
People with these characteristics we call "clairvoyants". The clairvoyant can "read" this information and can get in touch with our spirit guides and guardian angel. The clairvoyant can get in touch with deceased family members, friends and other deceased who have a message for help in the situation, the client is in.
It should be noted that the RV is not "call" to the deceased, but they do present themselves to help the clairvoyant, if necessary. Clairvoyance must not be confused with spiritualism and magic where one summons dead in different ways.
We all have a guardian angel, one or more spiritual guides and a higher self. They are our contact with the spiritual world. We all have an inner wisdom and intuition, but all of of don’t get to equally understand the signals emitted from the spiritual world, our guides and our guardian angel.
Therefore, one can make use of people with highly developed senses, having access to information, that are not physically there. It may be the clairvoyant advisor.