A fantasy is a situation imagined by an individual or group, which does not correspond with reality but expresses certain desires or aims of its creator. Fantasies typically involve situations which are impossible (such as the existence of magic powers) or highly unlikely (such as world peace). Fantasies can also be sexual in nature.
An adult who constantly seems to be living in a fantasy world may be considered a Walter Mitty character.
Fantasy is also a literary genre involving the development of common or popular fantasies.