A changeling, also historically referred to as an auf or oaf, is a human-like creature found throughout much of European folklore. A changeling was a substitute left by a supernatural being on kidnapping a human being. Sometimes the changeling was a 'stock', more often the changeling was a supernatural being made magically to look like the kidnapped human. Supernatural beings blamed for stealing children included fairies, demons, trolls, nereids and many others. Usually, the kidnapped human was a child; but there were cases, particularly in Scandinavia and Ireland, where adults were taken.

A fairy is a type of mythical being or legendary creature, generally described as anthropomorphic, found in the folklore of multiple European cultures, a form of spirit, often with metaphysical, supernatural, or preternatural qualities.