Shamans are a type of religious specialist who uses altered states of consciousness to directly interact with gods and supernatural agents. Shamans are usually part time practitioners, who are part supernatural beings, at least some of the time. Shamans are generally associated with hunter-gatherer level societies.
Shamans, Festishes and Liminality
Shamans have special fetishes and their iconography (the symbols they use) include liminal creatures-creatures that are part-human, part-god, and/or part-animal; creatures that like the shaman him or herself are part in the mundane world, part in the otherwise inaccessible world of the gods. Shamans own individual tools of their trade-pipes, noisemakers, sucking tubes. They have private spaces and control access to shrines, which are in general small in size and unavailable to the public, such as caves, shrines, or natural sanctuaries.
A shaman may have annual rituals, but by and large they are sought out by members of their societies to perform special, personal rites, such as for healing rituals, or personal problems, or for finding game.
This definition of shaman is a traditional one used by anthropologists to put a name on something that is eccentric to each social group. The definition is also used to express a relative level of complexity in a given society. Shamans are at one end of a defined spectrum of religious specialists; priests are at the other. Societies create the religious specialists they use, and they don't use anthropological rules to tell them how to do it.
See the entry on Altered States of Consciousness for more information.
VanPool, Christine n.d. The signs of the sacred: Identifying shamans using archaeological evidence. Journal of Anthropological Archaeology in press.