An elemental is a demon of immense power, the most powerful type of all demons.
Elementals are created when powerful formations such as ice rivers or mountains die. Due to their enormous size, the spirits of these structures are exceptionally powerful as they were very powerful in life. Demons formed from the death of these formations thus have more power than any other demon.
In Wolf Brother, the demon bear which killed Torak's father had an Elemental demon trapped inside it, this made it very powerful and very dangerous.