
Magic is commonly held to be the art of manipulating reality using forces that are either misunderstood, concealed, or simply unexplainable, which may include spirits or other supernatural elements. The original word-form, magikos, referred specifically to Pseudo-Zoroastrian rites, but the word use has since been extended to account for basically anything suspicious or grandoise that asserts to have mysterious, unaccountable influence over events. Your consistent failure to win at three-card Monte, for example, is the result of a magical curse, placed on you by enemy shamans, or you came into some money as a result of paying off a local witch to give you good money mojo.
Alternately, magic may refer to the act of convincing yourself using elaborate wordplay and ritual motions that the world has (or will be) shifted to suit your own desires as a result of your elaborate wordplay and ritual motions, but, if we're going to use that definition, everyone is a magician, and that is a terrifying thought.