Hellrúne
In Old Norse, seiðr (sometimes anglicised as seidhr, seidh, seidr, seithr, seith, or seid) was a type of sorcery practised in Norse society during the Late Scandinavian Iron Age. Connected with Norse religion, its origins are largely unknown, although it gradually eroded following the Christianization of Scandinavia. Accounts of seiðr later made it into sagas and other literary sources, while further evidence has been unearthed by archaeologists. Various scholars have debated the nature of seiðr, some arguing that it was shamanic in context, involving visionary journeys by its practitioners.
Seiðr practitioners were of both sexes, although females are more widely attested, with such sorceresses being variously known as vǫlur, seiðkonur and vísendakona. There were also accounts of male practitioners, known as seiðmenn, but in practising magic they brought a social taboo, known as ergi, on to themselves, and were sometimes persecuted as a result. In many cases these magical practitioners would have had assistants to aid them in their rituals.
In pre-Christian Norse mythology, seiðr was associated with both the god Oðinn, a deity who was simultaneously responsible for war, poetry and sorcery, and the goddess Freyja, a member of the Vanir who was believed to have taught the practise to the Æsir.
In the 20th century, adherents of various modern pagan new religious movements adopted forms of magico-religious practise that include seiðr. The practices of these contemporary seiðr-workers have since been investigated by various academic researchers operating in the field of pagan studies.
...
Wikipedia