A hag is a old woman, or a kind of fairy or goddess having the appearance of such a woman, often found in folklore and children's tales such as Hansel and Gretel. Hags are often seen as malevolent, but may also be one of the chosen forms of shapeshifting deities, such as the Morrígan or Badb, who are seen as neither wholly beneficent nor malevolent.
The term appears in Middle English, and was a shortening of hægtesse, an Old English term for witch, similarly the Dutch heks and German Hexe are also shortenings, of the Middle Dutch haghetisse and Old High German hagzusa respectively. All these words derive from the Proto-Germanic *hagatusjon- which is of unknown origin, however the first element may be related to the word "hedge". As a in fairy or folk tale, the hag shares characteristics with the crone, and the two words are sometimes used as if interchangeable.
Using the word "hag" to translate terms found in non-English (or non-modern English) is contentious, since use of the word is often associated with misogyny.
A hag, or "the Old Hag", was a nightmare spirit in English and anglophone North American folklore. This variety of hag is essentially identical to the Old English mæra—a being with roots in ancient Germanic superstition, and closely related to the Scandinavian mara. According to folklore, the Old Hag sat on a sleeper's chest and sent nightmares to him or her. When the subject awoke, he or she would be unable to breathe or even move for a short period of time. In the Swedish film Marianne, the main character suffers from these nightmares. This state is now called sleep paralysis, but in the old belief the subject had been "hagridden". It is still frequently discussed as if it were a paranormal state.