The term "mana" is bandied about in numerous role-playing games as a generic term for a sort of impersonal magical energy. i.e. A magician charges up his mana batteries and then drains them in casting off a spell. While I am not really worried that people really believe this, I think it is good to know what the term really means.
Scholars in the 19th and early 20th centuries compared this portrait of mana to other religious phenomena they believed to be parallel, especially wakan and orenda among the Dakota (Sioux) and Iroquois Indians. From these anthropologists in the early part of the 20th century developed the theory that mana was a worldwide phenomenon that lay behind all religions but was later supplanted by personified forces and deities.
Subsequent scholarship has challenged both the original description of mana and the conclusions drawn from it. Mana is by no means universal; it is not even common to all of Melanesia; many of the parallels that have been adduced have been found to be specious. Mana is not impersonal. It is never spoken of by itself but always in connection with powerful beings or things. Thus, mana would seem to be descriptive of the possession of power and not itself the source of power. Rather than being an impersonal power, mana is inextricably related to belief in spirits.
Among contemporary scholars a functionalist and political interpretation has been offered. Mana is not found within relatively simple tribes but rather in the more highly organized Melanesian societies. It would seem to be a symbolic way of expressing the special qualities attributed to persons of status and authority in a society, of providing sanction for their actions, and of explaining their failures.