"Most of my hag volunteers have refrained from taking a bite out of me since last Tuesday."
-- Professor Regulus Moonshine, somewhat optimistically (DP4)
Hags are female magical beings with somewhat evil tendencies, similar to humans but less adept than witches at disguising themselves from Muggles (GF19). The book The Dark Forces: A Guide to Self-Protection describes a hag as “a child-eating creature of human appearance, though likely to have more warts than the average witch” (Pm). Information from the 2nd and 3rd W.O.M.B.A.T. tests show that hags eat small children and have four toes on each foot, but have only rudimentary magic, similar to that observed in trolls. The Ministry is said to consider Hags to be “less dangerous” than Werewolves and Inferi (JKR-W2, JKR-W3).
Hags are wild in appearance, and they have been known to eat children (FB, DP4, FW), although at the Leaky Cauldron Harry once saw a hag eating raw liver (PA4). Hags can be quite frightening, apparently, since Quirrell had a “nasty bit of business” with one during his year off for first-hand experience in fighting the Dark Arts (PS5). Interested parties may also consult Gilderoy Lockhart‘s book Holidays with Hags (CS4), which probably can be picked up quite cheaply at Flourish and Blotts these days.
In the mid-1990s, Professor Regulus Moonshine claimed to have discovered a potion to reduce a hag’s craving for human flesh. Moonshine’s extensive injuries — several chunks of his face and neck had been bitten off — suggested that his research had not been without peril (DP4).
In the late 1600s-early 1700s, Honoria Nutcombe founded the Society for the Reformation of Hags (FW).
Known hags include:
The word "hag" has referred to a witch or a repulsive old woman since the 13th century. The origins of the word are obscure, but it is connected to the word for "hedge." A witch was considered to be a "hedge-rider" where the hedge was seen as the dividing line between the cultivated, civilized world and the wilderness beyond. A hag, then, is someone who lives in both realities.
Hags are the wizarding world's equivalent of "fairy tale witches." There was no masculine form of the word, and all the witches in fairy tales are depicted as women. Rowling's hags also seem to be exclusively female.
From the Web
What is a hag in Harry Potter from the Science Fiction and Fantasy Stack Exchange