In the study of mythology, mana refers to a supernatural force said to exist within all things, sometimes associated with maternal and lunar magic. The word originally stems from an anthropologist's understanding of the word mana in Polynesian religion.
Mana is the power of magic, and of all talismans and fetishes, whether devoted to ancient gods, Roman Catholic saint relics, the spirits of the ancestors, or the underlying element that makes up the universe and all life within it as in European alchemy.
In some fantasy settings and games, mana is a natural energy resource which is used or channeled by wizards to cast spells. This use of the term was coined by Larry Niven in his 1978 novella The Magic Goes Away, which deals with mana as a limited natural resource, becoming depleted.
Mana in this sense has been used in numerous role-playing games and computer role-playing gamess (e.g., GURPS and Diablo series), trading card games (Magic: The Gathering), MUDs and MMORPGs (EverQuest), and strategy games (StarCraft and Warcraft series).
Mana is also the name of a rather expensive 'hi-fi rack'.