Blue Magic is a type of
magic used in
RPG's, specifically
Final Fantasy and
Final Fantasy Tactics games. It was named "blue" magic perhaps to differentiate it from
black magic and
white magic, and to differentiate also between black, white and
red mages, which are conventions as old as the
Final Fantasy series.
Blue Magic refers to magic that is used by monsters in RPG's, and thus is usually unavailable to player characters. A blue mage usually has to learn these special spells by getting hit with them in battle by monsters that cast them before they are learned and available for use, though in some Final Fantasies they can be purchased from magic shops.
It has been said that blue magic is powerful, but that the casting cost is usually higher than normal black or white magics.