Hel is usually describes as a collection, tradition or type of Cosmology. Hel is characterised by the presence of Devils and/or Demons, almost always viewed as reprehensible and monstrous to the denizens of Materia. Many Hels have existed throughout history, some only known or documented in certain regions.
Throughout history, there have been some attempts to destroy or clear out the planes of Hel of monsters by marching armies into them either as a short campaign or to establish fortresses or armed realms of their own there (marches). This kind of incursion is known as a Helmarch.