What is "Spiritualism?"
I think that the concept of "spiritualism" has become assigned to the worship of a transcendental being or process that lies outside the domain of established and "traditional" religion. One finds that people can possess "spirituality" without belonging to a formal denomination or congregation of individuals. The emphasis is on "spiritual" here. The individual who aspires to a "spiritual" path is one who seeks to enhance their own understanding of themselves in the world and a connection with something transcendent, but selects to do so in a manner that is away from something organized in terms of a collective entity. People can still be spiritual even if they align themselves with this established and formal entity. Yet, the idea of "spiritualism" as it is seen today is one whereby individuals seek to find their own path to connection with something more than them in a domain that is not so embedded in formality and organized structure. The pursuit of an "immaterial" reality becomes an individualized quest, as opposed to one driven by collectivity and traditionalist approaches.
Spiritualism is a religion that is not based on a relationship with a particular savior. It recognizes all prophets that have come to humankind throughout the ages, not setting one above the other.
Spiritualism is a monotheistic belief system or religion, postulating a belief in God but not an anthropomorphic one. A distinguishing feature is the belief that spirits of the dead residing in the spirit world have both the ability and the inclination to communicate with the living. Anyone may receive spirit messages, but formal communication sessions are held by "mediums", who can then provide information about the afterlife.