The word “shaman” refers to a person who journeys to non-ordinary worlds or realities in an altered state of consciousness.
In his book, “Shamanism: Archaic Techniques of Ecstasy,” Mircea Eliade concludes that
Shamanism underlays all the other spiritual traditions on the planet, and that the most distinctive feature of shamanism — but by no means the only one — was the journey to other worlds in an altered state of consciousness.
Shamanism is not a belief system. It’s a system of knowledge that’s based on personal experience. The shaman journeys and brings back information (healing, spiritual truths, etc.) for his tribe.
“Shamanic Healing: We Are Not Alone.” An Interview of Michael Harner by Bonnie Horrigan, 1997. Available here.