A medium is someone who is able to communicate to the spirits of people or animals who have passed over. Every Medium has the psychic ability but not every psychic has the ability to communicator with those who are deceased.
And from my experience not every medium can comminicate with Animals. it maybe dorment in some mediums and not in others.
mediums and the connection with the after life Has been discussed throughout history many different cultures believed in the after life and there are Stories such as in the old testiment.
mediums became popular back in the 19th century around that time spiritualism became known. and people such as egar cayce were important in getting the exists of mediums and psychics known.
Since then mediumship is more well known although people do confuse Clairvoyant And mediumship. Clairvoyant is the abillty to see images in the minds eye. it is a common way for mediums and psychic to recieve messages